WinCC Upgrade Tag Loss: Resolving V4.x to V5.x Disappearing Tags

Problem Overview

When migrating a Siemens WinCC project from V4.x to V5.1 SP1 (or any V5.x target), engineers frequently report that the migrated database opens without errors, but the tag editor shows zero entries — or a substantial subset of the original tag set (commonly 800–1,200 tags on a typical SIMATIC S7 MPI project) is missing. Internal cross-references in pictures, scripts, and archive configurations that point to the lost tag names evaluate to address 0 and raise runtime errors.

The migration tool Project Migrator completes the .mcp → .mdf database conversion, the picture tree rebuilds, the user administration migrates, and the alarm logging / tag logging archives copy forward. The only loss is the population of the Tags table inside the runtime database. This single symptom is misleading because the Tag Management dialog appears to be intact, the channel unit is present, and the connection (e.g., MPI under SIMATIC S7 Protocol Suite) is still listed — but it is empty.

Affected Versions and Tooling

Root Cause Analysis

Three root causes account for the vast majority of V4.x → V5.x tag-loss incidents. Treat them as a layered checklist; one or more may apply to a given project.

1. Channel Not Authorized in the Target License / Release

WinCC V5.x enforces a tag-count and channel-license gate at project-open time. If the original V4.x project referenced a channel DLL that is present in V4.x but excluded, renamed, or downgraded in the V5.x installation (for example, a third-party OPC channel, a redundant channel, or a non-licensed PROFIBUS-FDL channel), the channel unit is silently stripped during migration, and all child tags disappear with it. The dialog shows no error — only an empty tree.

Open the original V4.x project on a machine that still has V4.x installed and inspect Tag Management > [Channel]. Note every channel DLL and every connection. Cross-check that each DLL is installed in the V5.x \bin folder and licensed on the new Authorization disk. If any DLL is missing, install the matching add-on package (e.g., SIMATIC S7 Protocol Suite, OPC Channel) from the V5.x DVD before attempting the upgrade.

2. SIMATIC S7 Protocol Suite Unit Lost During DB Bind

For the most common case — a project with a single MPI connection under the SIMATIC S7 Protocol Suite — the channel DLL S7CHN.dll is present, the connection is created, but the migration tool does not re-attach the Tags table fragment to the new connection. This is most often caused by a mismatch in the Connection parameters > S7-Network Address > Station Address field, where a value that V4.x tolerated (e.g., trailing whitespace, lowercase hex) is rejected by V5.x validation, causing the connection to fail to bind at upgrade time.

Procedure:

1. In V5.1, right-click the MPI connection → Properties.
2. Confirm Station Address parses as a plain decimal integer in the range 0–126 for MPI, or 0–127 for PROFIBUS.
3. Confirm Segment matches the physically configured MPI segment (default 1, segment 0 for direct PG/PC connection).
4. Re-enter the address if any anomaly is visible, then save the project. The tag table re-binds on next project activation.

3. Underlying Database Schema Mismatch

V4.x stored the runtime tag list in a binary blob inside the project file, whereas V5.x persists tags in SQL Server tables (dbo.TAG, dbo.TAGTEXT, dbo.TAGATTR). If the Project Migrator cannot translate a tag attribute it does not recognize — typically a custom data type, an extended Length field, or a Quality Code parameter from a non-Siemens channel — the migration aborts the import of that record and continues. The result: most tags arrive, but a subset vanishes silently.

Inspect the migration log: Start > Programs > SIMATIC > WinCC > Tools > Project Migrator then click View Log. Search for WARN and ERR entries referencing tag IDs. Each ERR line identifies a tag that failed to migrate and is the candidate for manual re-creation.

Recovery Procedure A: Re-export from V4.x with varexim.exe

This is the cleanest path. It assumes a working V4.x installation is available (or a virtual machine snapshot of one). The varexim.exe utility — sometimes called the Tag Export/Import smart tool — serializes the tag table to a CSV-like text file that V5.x can re-import cleanly.

Step 1 — Export on V4.x

1. Start WinCC Explorer on the V4.x host.
2. Close all editors that hold tag references.
3. Open a command prompt and navigate to %WinCC%\bin (V4.x path: \Siemens\WinCC\bin).
4. Execute:
   varexim.exe /export "C:\Export\V4tags.csv" /type tags /channel "SIMATIC S7 Protocol Suite\MPI"
5. Open the CSV in Notepad and verify the header row contains: Name;Type;Length;Address;FormatConversion;Scaling;Limit;InitialValue;Replace (V4.x uses semicolon delimiters; the column order is fixed and must not be edited).

Step 2 — Transfer to V5.x

1. Copy the CSV to the V5.x host (network share, USB, RDP mapped drive).
2. Place it in a path without spaces, e.g., D:\Migration\V4tags.csv. Spaces in the path break the V5.x varexim parser in SP1.

Step 3 — Import on V5.x

1. Open the migrated V5.1 SP1 project in the WinCC Explorer.
2. Confirm the target channel and connection exist (e.g., SIMATIC S7 Protocol Suite > MPI). Create the connection manually if it is missing — match the Station Address, Rack, Slot to the V4.x values exactly.
3. Close all tag-group views in the editor.
4. Run:
   varexim.exe /import "D:\Migration\V4tags.csv" /type tags /channel "SIMATIC S7 Protocol Suite\MPI"
5. The tool reports a summary: Imported: NNNN / Skipped: N / Errors: N. Zero errors is the success target.

Step 4 — Validate

1. In WinCC Explorer, right-click the Tags node under the MPI connection and select Properties. The tag count should match the V4.x source.
2. Open Tools > Cross Reference and re-link any picture object, script, or archive field that points to a now-recreated tag. Cross-references written by V4.x sometimes contain a numeric ID (TagID:4721) rather than the symbolic name; varexim re-issues the IDs and the old IDs become invalid.
3. Activate the project in test mode (Runtime > Start > Test Mode) and verify a known tag updates from the PLC.

Recovery Procedure B: Rebuild from Project Migrator Log

If a V4.x host is no longer available, the only source of truth is the migration log captured in V5.x.

1. Open Start > Programs > SIMATIC > WinCC > Tools > Project Migrator.
2. Click Open Log and load ProjectMig.log from \<ProjectName>\Migrate\.
3. Filter for lines matching Tag '.*' could not be migrated. Each line names a tag, its original channel, and a WinCC error number (commonly 0x80040E21, 0x80040E14).
4. Recreate the listed tags manually in the V5.x tag editor. The error code is the spec for what is wrong:

Verification Checklist

• Tag count parity: Tag Management > right-click root > Properties. The displayed count must equal the V4.x source count (or the V4.x source count minus tags that intentionally point to uninstalled channels).
• PLC round-trip test: In WinCC Runtime, write a known value to a writable tag and confirm the change is visible in STEP 7 online monitor on the matching DB / Merker / E/A address.
• Cross-reference integrity: Tools > Cross Reference should show zero entries flagged with a red exclamation mark. A red mark indicates a tag ID reference that no longer resolves.
• Archive replay: If the project used Tag Logging, open the Tag Logging Editor and confirm every archive references a valid tag. A missing tag appears as <undefined> in the archive configuration.
• Alarm logging: Open Alarm Logging Editor and re-link any message that referenced a lost tag; the Acknowledgement tag and State tag columns are typical loss points.

Prevention: Pre-Upgrade Audit

Run this audit on the V4.x project before initiating any V5.x migration. Each item is a one-time check that prevents an after-the-fact scramble.

1. Inventory channels. List every channel unit, the DLL backing it, and the connection count. Verify each DLL is on the V5.x installation media.
2. Inventory non-standard tag types. Open Tag Management > Properties on each tag group. Tag any with Type = Raw Data Type or custom user types — these are the highest-risk rows for V5.x translation.
3. Snapshot the tag list. Run varexim.exe /export once before migration, store the CSV in source control, and compare post-migration.
4. Validate addresses. Use STEP 7 to confirm that every DB and Merker address referenced by a tag still exists. Orphan addresses are valid syntax but unbind on first runtime start.
5. Back up the .mcp file. Keep the original V4.x project file in a versioned archive. The migration is one-way; the .mcp is the only path back.
6. Test on a clone. Copy the .mcp to a sandbox, run the migrator, and verify tag count parity before touching production.

Related Issue: V7.5 SP2 Tag Display Regression

The same symptom — configured tags not displayed in the tag editor — recurred in WinCC V7.5 SP2 as a confirmed product defect. The official Siemens entry SIOS 109794416 — Why are all configured tags no longer displayed after the WinCC upgrade to V7.5 SP2? documents that the issue is resolved by installing WinCC V7.5 SP2 Update2. The mechanics are different (a UI cache invalidation rather than a database schema migration) but the diagnostic shape is identical: tags exist in the database, the tag management dialog opens, the tree is empty. If a project is later upgraded past V5.x toward V6.x, V7.x, or TIA Portal WinCC Professional, apply the corresponding cumulative updates before declaring the migration a failure.

OPC Migration Path (for Unlicensed Channel Owners)

If a tag is hosted on a channel that is unavailable in the target V5.x license, the recommended remediation is to migrate the tags to the OPC channel. Procedure:

1. On the V4.x host, install the OPC Channel from the V4.x installation media (it is included even if unlicensed in run-time — it is licensed at the OPC server level).
2. Run varexim.exe /export as above.
3. On the V5.x host, create a OPC channel unit and an OPC group that matches the source connection name.
4. Import the CSV with the OPC channel as the target.
5. Reconfigure the OPC DA server (e.g., SIMATIC NET OPC Server, WinCC OPC Server) to publish the same item names.

This path is also the bridge for SCADA-to-SCADA migrations where a customer is consolidating on a newer WinCC version or moving to TIA Portal WinCC Professional V16/V17/V18 and needs the legacy V5.x tags to remain addressable.

Troubleshooting Matrix

Field-Proven Caveats

• The Test Mode runtime does not validate cross-references; a successful test-mode start is not proof that the migration succeeded. Always use Cross Reference for a static check.
• varexim.exe is a single-threaded tool. It cannot be safely run against a project while the WinCC Runtime is active. Stop the runtime before any export or import.
• Tag names in V4.x are case-preserved and case-insensitive. V5.x retains the same behavior, but varexim is case-sensitive on import. A tag named Motor_On in V4.x will not be deduped against a pre-existing motor_on in V5.x — both will exist, and runtime will pick the first match it encounters.
• Projects with more than 8,000 tags benefit from splitting the CSV by channel before import. varexim does not chunk transactions; a 30,000-row import with a single corrupt row can roll back the entire batch on SQL Server 2000.
• Always verify the resulting tag count via the V5.x Tag Management > Properties dialog and against the V4.x source count. The runtime Status > Tags view shows the count only for tags currently being polled, which can be a subset.

FAQ