Resolving Simatic Manager LAD to STL Conversion Error After Copying STEP 7 Projects

When a STEP 7 project developed in Ladder (LAD) is copied from one engineering workstation to another, engineers frequently encounter a persistent issue: blocks that were originally created in LAD open only in Statement List (STL) view, and the View > LAD menu command does nothing. The block compiles and runs, but the source representation is locked to STL and the ladder network cannot be restored through the user interface alone.

This article documents the underlying cause, three reliable remediation procedures, the project file structure involved, and the verification steps that confirm a clean fix. The procedures apply to STEP 7 V5.5 / V5.6 in the SIMATIC Manager environment (sometimes referred to as STEP 7 Classic), the standard toolchain for SIMATIC S7-300, S7-400, and WinAC controllers. For TIA Portal (STEP 7 Basic / Professional V13 and later) the equivalent issue is rare because the editor stores the source representation in the project file directly, but engineers migrating older S7 Classic projects frequently hit this problem during the copy or upgrade cycle.

1. Problem Description and Symptoms

1.1 Observable Behavior

• An S7 project copied via Windows Explorer (drag-and-drop, USB stick, network share, or compressed folder) opens normally in SIMATIC Manager.
• Organization Blocks (OB), Function Blocks (FB), Functions (FC), and System Function Blocks (SFB) that were originally written in LAD open in STL view only.
• Selecting View > LAD, View > FBD, or clicking the LAD icon in the toolbar has no effect. The editor remains in STL.
• No compile error, no warning, no fault indicator appears in the diagnostic buffer. The block is functionally correct and downloads to the CPU without issue.
• Closing and reopening the block does not restore the LAD view.
• In the cross-reference and program structure, the block is listed as a valid program element but its representation flag is set to STL.

1.2 The Conversion Path

When a block cannot be displayed in its native language, SIMATIC Manager automatically downgrades the view to STL because STL is the only language guaranteed to round-trip from any other representation. LAD and FBD are graphical languages that depend on the original schematic, while STL is textual and reflects the compiled mnemonic. If the editor cannot confirm that the source was stored as a LAD network, it falls back to STL to guarantee that the engineer can still read the logic.

1.3 When the Issue Occurs

The most common trigger is a direct file-system copy of the project folder while SIMATIC Manager is closed, particularly when:

• Two workstations have different STEP 7 versions installed (for example, V5.5 SP1 on the source, V5.4 SP5 on the target).
• The project was originally saved on a workstation with a non-default Editor tab setting where Type check of addresses is enabled.
• The Language file inside the project's Global directory is missing, truncated, or not transferred with the rest of the folder.
• The Family and Version tags inside the block container do not match the registered languages of the target editor installation.

2. Root Cause Analysis

2.1 The SIMATIC Manager Block Representation Model

Every code block in an S7 Classic project may exist in up to three different language representations, depending on the languages installed on the engineering station:

When a block is created in LAD, SIMATIC Manager stores three artifacts: the compiled STL (the canonical form loaded into the CPU), an optional LAD network source, and an optional FBD network source. On a fresh workstation, the editor inspects the Language file in the Global directory to determine which representations are present. If the file is absent or unreadable, the editor assumes only STL is available and opens every block as text.

2.2 The Language File

Inside every S7 project, the directory <ProjectName>\Global contains a binary file named Language (no extension). This file maps each block to its allowed language representations using internal object IDs. The file is regenerated whenever a block is saved with a new representation, and it is read whenever the project is opened.

If the file is:

• Missing — SIMATIC Manager prompts for a regeneration or falls back to STL only.
• Corrupted — the editor treats every block as STL, regardless of the actual source.
• Stale — the editor may show STL for blocks that have a valid LAD source but whose representation flag is not registered.

2.3 The Address Type Check Setting

The Type check of addresses option in Options > Customize > LAD/FBD tab enforces strict typing on LAD/FBD networks. When enabled, the editor will refuse to display a block in LAD if it contains an address whose symbolic or absolute type is ambiguous, even if the original LAD source was perfectly valid. This setting is stored per workstation in the registry, not in the project, so a project created on a workstation with strict checking may fail to open in LAD on a workstation with the same setting disabled, and vice versa.

2.4 Why Drag-and-Drop Copy Is Risky

Windows Explorer copy does not respect SIMATIC Manager's notion of a project as a transactional unit. The project may be copied while the source workstation still has a read-write handle to the Language file, or the destination may receive a partial copy if the source was being saved at that moment. The proper migration mechanism is the Archive ↔ Retrieve workflow, which packages the project as a single .zip-based archive and unpacks it transactionally on the target.

3. STEP 7 Project Structure Reference

Understanding the layout is essential for the manual remediation in Solution 1.

3.1 Top-Level Directory

An S7 Classic project is a Windows folder whose name matches the project name. Example: C:\S7Projects\ConveyorLine\. The folder contains a project file ConveyorLine.s7p and the following subdirectories:

3.2 The Global Folder in Detail

The Global folder is where the Language file lives. The file has no extension and is small (typically 1–8 KB even for large projects). It is binary, not editable in a text editor, and is created/updated automatically by SIMATIC Manager.

3.3 Block Storage Locations

Compiled blocks live in S7Program\Blocks. Each block is a binary file with a numeric name (for example, FC1, OB1, DB10) and may have associated source files in Global\Sources with extensions .awl (STL), .scl (SCL), or .graph (GRAPH). LAD and FBD sources are not stored as external files; they are embedded in the Language metadata inside the block container itself.

4. Solution 1 — Delete the Language File and Re-save with Reorganization

This is the most reliable field-proven procedure and matches the fix confirmed by the original engineer on the forum thread.

4.1 Prerequisites

• Close SIMATIC Manager and SFC / S7 Graph editors.
• Verify the project is not open on any other workstation (network share — close any read handles).
• Make a full backup of the project folder. Copy it to <ProjectName>_backup_YYYYMMDD\.

4.2 Step-by-Step

1. In Windows Explorer, navigate to the project root: C:\S7Projects\<ProjectName>\.
2. Open the Global subfolder.
3. Locate the file named Language (no extension). It is hidden by default — enable Show hidden files in Folder Options if needed.
4. Right-click the file and select Delete. Confirm the deletion.
5. Do not delete any other file in Global. The symbol table (Symbols), source files, and system data blocks must remain intact.
6. Launch SIMATIC Manager and open the project. SIMATIC Manager will detect the missing file and regenerate it on the first save.
7. Select the S7 Program node in the project tree, or the entire <ProjectName> node.
8. From the menu, choose File > Save As.
9. In the Save As dialog, check the option "with reorganization (slow)". This forces a complete rewrite of all block metadata, including the language representation tags.
10. Click OK. The save may take several minutes for large projects; the progress bar indicates the active block.
11. When the save completes, open any block that was previously shown as STL. The LAD view should now be selectable and active.

4.3 What "Reorganization" Does

The reorganization option performs a full garbage-collection pass on the project database. It rebuilds the cross-reference data, regenerates the Language file from the actual block contents, and resolves any inconsistencies in the block container headers. This is the same mechanism SIMATIC Manager uses after a STEP 7 service pack upgrade.

4.4 Verification

• Open the previously affected block.
• Click the LAD icon in the toolbar — the block should switch to ladder view.
• Click FBD — the block should switch to function block diagram view.
• Click STL — the block should switch back to statement list.
• Repeat for every block that was reported as STL-only.

5. Solution 2 — Disable the Address Type Check

This solution was independently confirmed by another engineer in the same discussion and is often faster than Solution 1 for projects with only a few affected blocks.

5.1 When to Apply

Apply this solution when:

• Solution 1 has been applied but specific blocks still refuse to display in LAD.
• The blocks contain symbolic addresses with multiple possible data types (for example, a block parameter typed as BLOCK_FC or POINTER).
• The issue is reproducible on a single workstation only and not on the original development machine.

5.2 Step-by-Step

1. Open SIMATIC Manager and load the project.
2. In the project tree, double-click any block to open the editor (it does not matter which block — the goal is to access the menu).
3. From the menu bar, select Options > Customize.
4. In the Customize dialog, click the LAD/FBD tab.
5. Locate the checkbox "Type check of addresses".
6. Uncheck the box. Click OK to apply.
7. Close the block and reopen the previously affected block. The LAD view should now be active.

5.3 What the Setting Controls

The Type check of addresses option enables strict type validation in the LAD and FBD editors. When enabled, the editor will not allow a block to be displayed in graphical form if any address in the network has a type that cannot be unambiguously resolved (for example, an ANY pointer, an untyped formal parameter, or a multi-instance DB). Disabling the check relaxes this constraint and allows the editor to render the block in LAD as long as a valid LAD source exists.

5.4 Caveat for Multi-User Projects

If multiple engineers work on the same project, be aware that this setting is stored in the Windows registry of the engineering workstation (HKCU\Software\Siemens\STEP7\2.0\Settings\LADFBD\TypeCheck in V5.5 and similar paths in other versions). Each engineer should configure the setting to match the project author's preference. The setting is not stored in the project file itself.

6. Solution 3 — Use Archive and Retrieve

The proper Siemens-recommended procedure for moving an S7 Classic project between workstations is to use the built-in archive and retrieve functions. This is the procedure that should be used to prevent the LAD-to-STL issue in the first place.

6.1 Archive Procedure (Source Workstation)

1. Open the project in SIMATIC Manager.
2. Select the project node in the project tree.
3. From the menu, choose File > Archive.
4. In the Archive dialog, browse to a temporary folder and enter a filename. The default extension is .zip for STEP 7 V5.5 and later; older versions used .arj.
5. Click Save. SIMATIC Manager creates a single compressed archive containing the entire project, including the Language file, all block containers, symbol tables, and source files.
6. Copy the archive to a USB stick, network share, or other transfer medium.

6.2 Retrieve Procedure (Target Workstation)

1. Copy the archive to the target workstation.
2. Open SIMATIC Manager. Do not create a new project.
3. From the menu, choose File > Retrieve.
4. Browse to the archive file and click Open
5. In the Select Destination Directory dialog, choose the folder where the project should be unpacked. SIMATIC Manager creates a subfolder with the project name.
6. Click OK. The project is unpacked transactionally, and the Language file is restored intact.

6.3 Why Archive and Retrieve Is Preferred

• Atomicity: The project is either fully extracted or not at all. Partial copies are impossible.
• Path-length safety: Archive extraction handles long Windows paths correctly; raw Explorer copy may fail on deeply nested blocks.
• Cross-version compatibility: The archive is forward-compatible within the V5.x line. A V5.4 archive can be retrieved on a V5.6 workstation and vice versa.
• Block metadata integrity: The Language file and block container headers are preserved bit-for-bit, eliminating the LAD-to-STL fallback.

7. Verification Procedures

After applying any of the three solutions, perform the following checks before declaring the issue resolved.

7.1 Block View Round-Trip Test

1. Open each previously affected block.
2. Switch through View > LAD, View > FBD, View > STL.
3. Confirm that all three views render without error.
4. Make a small change (insert a NOP 0 or a commented line), save the block, and reopen it. Confirm the view setting persists.

7.2 Project-Wide Compilation

1. Right-click the S7 Program node and select Compile > All Blocks.
2. Review the compile log. No new warnings should be introduced by the migration.
3. Open the Module Information of the target CPU (if online) and verify that the program is downloadable.

7.3 Cross-Reference Check

1. Select the S7 Program node and choose Options > Cross-Reference Data.
2. Confirm that the cross-reference display shows all blocks and that the Language column (or the language icon overlay) indicates the correct representation for each block.

7.4 Re-archive Test

Archive the project again on the target workstation, retrieve it on a third workstation, and confirm that LAD view is preserved end-to-end. This validates that the migration is complete and that the project can be shared with other engineers without re-introducing the issue.

8. Prevention Best Practices

8.1 Mandatory Archive/Retrieve Workflow

Institute a team-level rule: S7 Classic projects move between workstations only through archive and retrieve. Disable Windows Explorer copy of project folders in the team's standard operating procedure document. If a file share is used, store only the archive on the share, never the live project folder.

8.2 Version Pinning

Maintain a single STEP 7 version across all engineering workstations on a project team. Mixed versions are the most common source of the LAD-to-STL fallback. Document the required STEP 7 service pack level in the project header and enforce it through the team's setup checklist.

8.3 Editor Settings Baseline

Standardize the Options > Customize > LAD/FBD tab across the team. The recommended baseline for production projects is:

8.4 Periodic Reorganization

Perform a Save As with reorganization on the master project at every major project milestone (FAT, SAT, commissioning, handover). This keeps the project database compact and prevents the accumulation of stale metadata that can trigger the LAD-to-STL fallback.

8.5 Backup Strategy

Maintain a rolling backup of the project with at least three generations. Use the SIMATIC Manager Save As with reorganization output as the canonical backup, not the raw project folder, to ensure that the backup itself is consistent.

9. Related Issues and Edge Cases

9.1 Blocks Created in S7-GRAPH or S7-SCL

If a block was created in GRAPH (state machine) or SCL (high-level), the LAD and FBD views are not available regardless of the migration procedure. Only GRAPH or SCL view (and the canonical STL view) will be selectable. The LAD-to-STL fallback for these blocks is expected behavior, not a fault.

9.2 Know-How-Protected Blocks

Blocks protected with KNOW_HOW_PROTECT cannot be displayed in any graphical view. They open in STL only, and the source is encrypted in the block container. The LAD-to-STL issue does not apply to these blocks.

9.3 Multi-Instance and Multiple Instance DBs

Multi-instance data blocks created from FB instances may display address type ambiguity that triggers the type check failure. The standard remediation is Solution 2 (disable type check) combined with a review of the FB interface declaration to ensure that all instance parameters are explicitly typed.

9.4 Migrating from STEP 7 V4 to V5.5

Projects created in STEP 7 V4 (or earlier) and migrated to V5.x may carry forward block containers that use the older representation format. The Language file may not be present at all in the migrated project. Solution 1 is mandatory in this scenario and may need to be applied twice.

9.5 Projects with Integrated WinCC Flexible

Projects that include an integrated WinCC flexible HMI station have an additional hmi folder. The LAD-to-STL issue is unaffected by the HMI integration, but the archive procedure is — ensure that the HMI component is also archived (the SIMATIC Manager Archive command handles this automatically).

9.6 TIA Portal (STEP 7 V13+) vs. SIMATIC Manager

In TIA Portal, blocks are stored as XML files in the project directory and the language representation is explicit in the block attributes. The LAD-to-STL fallback is not possible in the same way. However, when migrating a SIMATIC Manager project into TIA Portal, the migrated blocks may open in STL if the converter cannot reconstruct the original LAD source. In this case, the fix is to open the block in TIA Portal and use Edit > Switch Programming Language > LAD, which forces a regeneration of the LAD source from the STL canonical form.

10. Troubleshooting Matrix

11. Diagnostic Quick-Check Procedure

When the issue is reported on a new project, run this 5-minute diagnostic to determine which solution applies.

1. Open SIMATIC Manager and load the project.
2. Right-click the project node and choose Object Properties. Note the Last modified timestamp and the Created with STEP 7 version field.
3. In Windows Explorer, navigate to the project's Global folder. Confirm the Language file exists. Note its size and timestamp.
4. Compare the Language file timestamp to the last save timestamp on the project. If the file is older than the most recent block save, the file is stale — Solution 1 applies.
5. Open any LAD block and check Options > Customize > LAD/FBD. If Type check of addresses is enabled and the block contains an ANY/POINTER parameter, Solution 2 applies.
6. If the project was last archived and retrieved, check the archive file's creation date. If the archive predates the issue, re-archive from the source — Solution 3 applies.

12. Reference: STEP 7 V5.5 / V5.6 Version Compatibility

Projects created in V5.5 SP4 can be opened in V5.6 without conversion. Projects created in V5.4 require the V5.4 SP5 compatibility patch to be installed on V5.5 or later workstations. Cross-version open is the second most common source of the LAD-to-STL fallback after Explorer copy.

13. Frequently Asked Questions