Resolving TIA Portal V18 Class SYMB TEXTCOMPOSER Compile Error

Resolving TIA Portal V18 Class SYMB TEXTCOMPOSER Compilation Error

The Class SYMB and TEXTCOMPOSER internal compiler error is one of the more obscure failure modes reported when building WinCC visualization projects in TIA Portal V18 with WinCC Basic / Comfort / Advanced V16/V17/V18. It typically surfaces in projects that combine many faceplates, language switching, large tag lists, and complex screen hierarchies. Unlike a missing tag or invalid reference, this error originates inside the HMI generator stage that builds the symbol database and text composer tables for the runtime image, leaving engineers with little diagnostic information beyond a generic failure message.

This reference walks through the known root cause hypotheses, the official Siemens mitigation procedure (reset of the IM folder), the platform compatibility trap that catches projects using faceplates on Basic Panels, and the field-proven workarounds used to recover projects when Siemens Support response is delayed. Every step is written for engineers who need to unblock a stalled build today.

1. Problem Description and Failure Mode

The error appears during the Compile and download or Compile step of an HMI device (panel or PC-based runtime). The compile log terminates with messages referencing Class SYMB and TEXTCOMPOSER internal modules, without a precise line number, screen name, or tag identifier. Typical accompanying symptoms:

• Compile halts in the HMI generation phase; PLC compile completes cleanly.
• Error is reproducible on the same source project but does not appear on a freshly created test project with the same elements.
• Removing screens or faceplates from the project eliminates the error, suggesting an internal generator limit or stale project cache.
• The error persists after a normal TIA Portal restart, after Project > Clean, and after removing the IM (Intermediate) folder manually using Windows Explorer while TIA is closed.

The diagnostic signature is the absence of a usable error message: TEXTCOMPOSER is invoked near the end of the build pipeline to assemble multilingual text fragments across faceplates, library references, and dynamic text lists. When the internal table exceeds the generator's capacity, or when an entry references a deleted/deleted-but-still-referenced object, the class returns a non-recoverable failure that is surfaced upward as a generic SYMB/TEXTCOMPOSER message.

2. Affected Versions and Environment

3. Root Cause Hypotheses

Siemens does not publish a single defect note that exactly matches this message string. Engineering analysis and field reports converge on three plausible causes; the third is the most common in practice.

3.1 Internal Generator Capacity Exceeded

TEXTCOMPOSER builds an in-memory table that pairs every displayable text token with its language variant, source object reference, and dynamic parameter list. When the project contains:

• > 30 faceplate instances or 15+ distinct faceplate types, and
• > 6 active runtime languages, and
• Deeply nested faceplate interfaces (faceplates referencing other faceplates),

...the table size or inter-object graph may exceed the generator's working allocation, producing a memory-allocation failure that surfaces as a SYMB/TEXTCOMPOSER error rather than a clean out-of-memory exception.

3.2 Stale References in the IM Folder

The IM (Intermediate) folder holds the generated cross-reference tables, cached symbol database, and incremental build artifacts. When a source object (faceplate, screen, library type, tag) is deleted but the IM folder still references it, the generator can dereference a NULL pointer inside SYMB or TEXTCOMPOSER. This is the case addressed by the official Siemens procedure referenced later in this article.

3.3 Target Device / License Mismatch

If the HMI device is configured as a Basic Panel (KTP400 Basic, KTP700 Basic, KTP1200 Basic) but the project contains faceplates, screens, or libraries that only exist for Comfort/Advanced targets, the project model is internally inconsistent. The compiler attempts to enumerate faceplate interfaces for a runtime that cannot host them, and TEXTCOMPOSER fails while iterating invalid symbol references. This is a configuration defect, not a generator defect, and must be corrected by retargeting the HMI device to a Comfort Panel, WinCC Runtime Advanced, or migrating the project to a configuration that does not use faceplates.

4. Diagnostic Workflow

4.1 Step-by-Step Diagnostic Procedure

1. Open Project Support Information via Project > Project support information and save the archive; this is the smallest reproducer that Siemens Support will request.
2. Confirm the exact TIA Portal version and updates: open Help > About TIA Portal and record the exact build string (for example V18.0 + SP1 + UPD4). Older updates within V18 are known to ship with bugs in the HMI generator.
3. Inspect the HMI device target: right-click the HMI device > Properties > General. Confirm the device family is Comfort Panel, WinCC Runtime Advanced, or WinCC Runtime Professional — not Basic Panel.
4. Count active faceplates and languages: Project tree > HMI > Faceplates and Project tree > Languages & Resources > Project languages. Record the totals.
5. Test compile a stripped copy: duplicate the project under a new name, delete half the screens, recompile. Repeat bisection until the offending screen or faceplate is isolated.

5. Official Siemens Mitigation: IM Folder Reset

Siemens publishes an explicit procedure to reset the IM folder that forces a full regeneration of the intermediate symbol and text composer tables. The procedure is documented in the Siemens Industry Online Support article referenced below. Always perform the procedure with TIA Portal fully closed; deleting the folder while TIA holds file handles can corrupt the project.

Procedure summary:

1. Close TIA Portal completely, including all instances and the TIA Portal background services.
2. Open the project folder in Windows Explorer. The IM folder is a sibling of .ap18 source file (or inside the project package after extraction).
3. Rename the IM folder to IM_old. Do not delete it yet — keep it for fallback.
4. Rename the Log folder to Log_old for the same reason.
5. Restart TIA Portal and open the project. TIA will rebuild the IM and Log folders during the next compile.
6. Compile the HMI device. If the error is resolved, the IM_old and Log_old folders can be deleted after a successful full project build and download.
7. If the error persists, restore IM_old / Log_old and proceed to the structural workarounds in the next section.

Reference: Siemens KB 109778709 – Reset of the IM folder in TIA Portal projects.

6. Structural Workarounds When Reset Fails

When the IM reset does not resolve the failure, the next hypothesis is exceeded generator capacity. Apply the reductions below in order, recompiling after each step to identify the smallest change that restores a clean build.

6.1 Reduce Active Runtime Languages

The text composer multiplies by the number of languages. Drop languages not strictly required for the current commissioning phase. Three languages is the typical comfort-zone threshold for faceplate-heavy projects; six is often the practical ceiling.

6.2 Convert Generic Faceplate Instances to Type Instances

When the same faceplate is instantiated many times, ensure you are using faceplate type instances, not hand-cloned duplicates. Type instances share a single definition and one TEXTCOMPOSER entry per type, whereas duplicates inflate the table multiplicatively. Use Right-click > Create faceplate instance from the type, never copy/paste of the rendered instance.

6.3 Split the Project

For projects approaching the practical limits above, split into multiple HMI devices (two Comfort Panels, or a Panel + a WinCC Runtime Advanced PC) so that the generator workload is partitioned. Each device is compiled independently and the symbol/text composer table is built per device.

6.4 Replace Dynamically-Generated Texts

Text lists with thousands of entries, especially when referenced from faceplate interfaces, are processed by TEXTCOMPOSER for every language. Replace with computed string tags where possible, or pre-generate and cache text indices.

7. Verification After Mitigation

Once the compile completes, validate the runtime artifacts before declaring the issue resolved.

1. Clean compile: rebuild the entire project, not just the modified HMI. PLC + HMI compile must both pass.
2. Check generated runtime file: <project>\IM\HMI\<device>\<language>\*.crt (Compact) or *.rtb files should be present and timestamp-current.
3. Download to target: confirm the full transfer completes and the runtime starts without fault.
4. Smoke test language switching: cycle every active language on a faceplate-heavy screen and confirm no placeholder or empty-string entries appear.
5. Audit faceplate integrity: open each faceplate type in the editor and confirm no warning markers appear in the project tree.

8. Known Defects and Firmware Notes

9. When to Escalate to Siemens Support

Open a Support Request through Siemens Industry Online Support when:

• The error persists after IM reset, language reduction, and faceplate instance cleanup.
• The error reproduces in a minimal project (1 faceplate, 1 screen, 1 language) — this strongly suggests a generator defect.
• You have already installed the latest UPD for your TIA version.

Attach the Project Support Information archive (Project > Project support information) and the compile log from <project>\Log\. Include the exact TIA build string and a description of the bisection steps already performed; this dramatically shortens time-to-resolution because the support engineer can skip the manual reproduction phase.

10. Preventive Practices for Faceplate-Heavy Projects

1. Establish a faceplate governance guideline: maximum nesting depth 2, maximum instances per screen 25, maximum distinct faceplate types per project 40.
2. Pin TIA Portal updates for the duration of a project; upgrade only at well-defined milestones and re-validate all faceplates after each upgrade.
3. Automate IM reset in the CI/CD loop: when building HMI artifacts via the Openness API, always wipe IM and Log folders before IProject.Load.
4. Reference faceplates from a library project, not from the master project. This isolates TEXTCOMPOSER work to a single, versioned library and reduces merge-related corruption.
5. Maintain a "golden" stripped project that builds cleanly; bisect failing projects by overlaying changes from the failing project onto the golden baseline.

11. Related Errors and How They Differ

12. Key Takeaways

• The Class SYMB / TEXTCOMPOSER error is almost never a single defect; it is the surface symptom of generator capacity, stale IM cache, or — most commonly — a Basic Panel mistakenly configured to host faceplates.
• Always verify the HMI device target supports faceplates before chasing generator defects.
• The IM reset procedure is the only documented Siemens mitigation and must be performed with TIA fully closed.
• Bisection by removing screens/faceplates is the most reliable way to recover a stalled project without losing engineering time.
• Attach Project Support Information + the compile log to every Siemens Support Request; this is what the support engineer will ask for first.

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