Resolving Siemens WinCC 7.4 WebNavigator Client Graphics Errors

After migrating a WinCC 7.4 SCADA server from Windows Server 2008 to Windows 10, an operations team observed that WebNavigator clients rendered faulty graphics. Out of ten client workstations, eight worked correctly, while two displayed corrupted or missing picture elements. The fault was eventually traced to inconsistent distribution of the Siemens HMI Symbol Library and stale WinCC Viewer RT plug-in components on the failing clients. This reference describes the full diagnostic, root-cause analysis, and resolution workflow that resolves this class of WinCC 7.4 WebNavigator client graphics error.

1. Problem Description and Symptoms

WebNavigator thin clients load published WinCC pictures over HTTP/HTTPS using the WebViewer control hosted in Internet Explorer (or the Edge IE Mode shim on Windows 10 22H2 and later). When the picture cache or plug-in catalog on a client is older than the server build, the WebViewer can fall back to placeholder rendering for any object that has been added, replaced, or updated on the server.

The reported failure pattern:

• Server: WinCC 7.4 running on Windows 10 (migrated from Windows Server 2008).
• Clients: 10 Windows 10 22H2 workstations with WebNavigator client + DataMonitor client V7.4 Update 19.
• 8 of 10 clients render the same picture correctly.
• 2 of 10 clients display missing symbols, blanked picture areas, or visually corrupt static graphics.
• A re-imaged client (clean Windows 10 Pro + Office + WebNavigator + DataMonitor V7.4 Upd 19) reproduces the fault on the same two screens.
• Fault appears in WinCC Viewer RT only; the WinCC single-user station on the same PC renders the picture correctly.

The defect is not random. The discrepancy is deterministic per client, which points at a local component mismatch rather than a network or server-side runtime issue.

2. Affected Versions and Components

The following matrix summarizes the components that participate in client-side picture rendering and which release streams are known to interact badly if they drift apart.

Whenever the server-side build number advances (a WinCC Update, a WebNavigator hotfix, or a re-issued symbol library) and a client does not receive the matching plug-in set, the client silently reverts to whatever version of the symbol library and custom control plug-ins is already cached under %LOCALAPPDATA%\Siemens\WebNavigator.

3. Root Cause Analysis

There are four overlapping root causes that produce this exact symptom set. They are not mutually exclusive; in the field most cases combine at least two.

3.1 Stale WebConfigurator Output

The WebConfigurator is the WinCC tool that writes the Web.config file, the plug-in manifest, the published picture set, and the WebNavigator client installer into the WebNavigator publishing folder. When the WinCC installation is updated, the WebConfigurator must be re-run; otherwise, the web installer it produces continues to deploy the previous plug-in generation to any new client. The symptom is that the two problem clients in the field were originally installed while the WebConfigurator was still pointing at a pre-update manifest, and the cached client payload is now permanently behind the server.

3.2 Missing or Outdated WebNavigator Plug-in on the Client

WebNavigator plug-ins are ActiveX controls and WinCC custom controls that the WebViewer downloads on first contact. The browser also caches them in the Temporary Internet Files folder. If the local cache is not invalidated after a server update, the browser re-uses the old ax_*.cab file and silently skips the newer one.

3.3 Siemens HMI Symbol Library Not Distributed

The Siemens HMI Symbol Library is a separately installable WinCC component that supplies the standard palette of motors, valves, pipes, fans, and 2D/3D icons. When a PDL picture uses a symbol from this library, the WebNavigator client must have the same library registered locally. If the symbol library was installed on the server but not on the WebNavigator client installer image, the symbol instances render as empty rectangles or are absent entirely.

3.4 Custom ActiveX / OCX Requiring Plugin Builder

If the picture uses a custom ActiveX or OCX control that is not part of the standard WinCC picture elements, the WebNavigator client receives an empty placeholder. The control must be packaged using the WebNavigator Plugin Builder and added to the WebNavigator client installation. The Plugin Builder workflow is documented in the WinCC Information System under the entry ID cited in Section 9.

4. Diagnostic Workflow

Run these steps in order. Each step isolates one of the four root causes above.

1. Confirm the symptom is local to the client. Open the same picture on a known-good client. If the picture is good, the server is exonerated. The fault is local to the failing client or to the WebConfigurator output that fed it.
2. Capture the WebViewer log. On the failing client, start WinCC Viewer RT with the -log switch ("C:\Program Files (x86)\Siemens\Automation\WinCC Viewer RT\WinCCViewerRT.exe" -log) and reproduce the picture. Look for entries that reference missing OCX/ActiveX controls, missing DLLs, or symbol library load errors.
3. Compare the published package. On the server, open <WinCC Project>\WebNavigator\Web\ and check the modification times of Web.config, SiemensHmiSymbolLibrary.dll, and the Plugins subfolder. If the last-modified timestamps predate the WinCC Update 19 install, the WebConfigurator has not been re-run.
4. Compare the client cache. On a working client and on a failing client, open %LOCALAPPDATA%\Temp\Siemens\WebNavigator\ and list the *.cab files. The SHA-1 of WebViewer.cab should match; if it does not, the client is running an older viewer generation.
5. Inspect browser cache. In Internet Explorer (or Edge IE Mode) choose Tools → Internet Options → General → Settings → View Files and look for SiemensHmiSymbolLibrary.dll and WebViewer.dll. Note the file version. Repeat on a good client and confirm they are identical.
6. Verify the Symbol Library registry entries. On a working client and the failing client, compare HKLM\SOFTWARE\WOW6432Node\Siemens\WinCC\WebNavigator\InstalledPlugins. A missing key on the failing client means the plug-in was never registered locally.
7. Check for custom controls. Open the original PDL picture in Graphics Designer on the server and select Tools → Cross Reference for any control that is not a standard WinCC picture element. If a third-party or custom ActiveX is referenced, it must be packaged with the Plugin Builder (Section 6.2).

5. Solution: Re-Run the WebConfigurator

The single highest-leverage action is to re-run the WebConfigurator on the server so that the published web content and the client installer payload are regenerated against the current WinCC build.

1. Open Start → Siemens Automation → WebNavigator → WebConfigurator on the WinCC server.
2. Select the WinCC project that hosts the WebNavigator server.
3. Walk through every page. The configurator regenerates Web.config, refreshes the picture package, and rewrites the client installer with the current plug-in set.
4. When the configurator reports "Configuration successfully completed", close it.
5. Re-publish the WinCC project: in WinCC Explorer right-click the project and choose Web Navigator → Publish. Accept the default picture set. Do not skip this step; the WebConfigurator writes the manifest, but Publish rebuilds the actual picture data.
6. From any client, open http://<server>/WebNavigator/ and confirm the new self-signed certificate prompt and the updated plug-in version are reported.

6. Solution: Repair or Reinstall the Failing Clients

6.1 Standard WebNavigator Client Reinstall

1. On the failing client, open Control Panel → Programs and Features.
2. Uninstall SIMATIC WinCC WebNavigator Client and SIMATIC WinCC DataMonitor Client in that order.
3. Delete the user-scoped cache: rd /s /q "%LOCALAPPDATA%\Siemens\WebNavigator".
4. Delete the IE cache: Internet Options → General → Delete → Temporary Internet Files and website files. Tick the box.
5. Reboot.
6. Reinstall WebNavigator Client and DataMonitor Client from the updated server-published installer at http://<server>/WebNavigator/setup.exe. Do not reuse an old setup.exe from a USB stick or a network share that pre-dates the WebConfigurator rebuild.
7. Open the project in WinCC Viewer RT and re-test the picture.

6.2 Custom ActiveX Controls — Plugin Builder

If diagnostic step 7 (Section 4) revealed a custom ActiveX, OCX, or custom WinCC Control in the picture, that control must be packaged for WebNavigator distribution. The Plugin Builder is documented in the WinCC Information System entry referenced in Section 9.

1. On the server, start Start → Siemens Automation → WebNavigator → Plugin Builder.
2. Add the custom .ocx or .dll to a new plug-in project.
3. Mark the plug-in as required so that the client installer pulls it automatically.
4. Build the plug-in package; the output is a .crp file that the WebConfigurator will copy into the published Plugins folder.
5. Re-run the WebConfigurator (Section 5) so the plug-in is included in the regenerated client installer.
6. Reinstall the WebNavigator Client on every workstation that uses the custom control, including the two problem clients.

7. Solution: Symbol Library Refresh on the Client

If diagnostic step 6 (Section 4) shows the SiemensHmiSymbolLibrary registry key is missing on the failing client, the symbol library was never registered. There are two valid paths.

Path A — Re-run the WebNavigator Client installer. When the WebConfigurator output is current (Section 5), the client installer includes the symbol library as a dependency. A clean reinstall of the WebNavigator Client registers it.

Path B — Manual registration from a known-good client. If the deployment is image-based and you cannot push a fresh installer, you can copy the symbol library files from a good client and register them manually.

1. From a known-good client, copy SiemensHmiSymbolLibrary.dll from C:\Program Files (x86)\Siemens\Automation\WinCC\WebNavigator\bin\ to the same path on the failing client.
2. Open an elevated cmd.exe on the failing client and run regsvr32 /s "C:\Program Files (x86)\Siemens\Automation\WinCC\WebNavigator\bin\SiemensHmiSymbolLibrary.dll".
3. Restart WinCC Viewer RT and re-test the picture.

8. Solution: Browser Cache and Internet Explorer Settings

Even after the server is fixed, a stale browser cache on the client will keep the client pinned to the old control generation. Apply the following baseline to every WebNavigator client and lock it down with Group Policy.

1. Open Internet Options → General → Settings → Caching → Automatically. Set the disk space to between 250 MB and 1 GB.
2. Open Internet Options → General → Delete and clear Temporary Internet Files, Cookies, and History.
3. Open Internet Options → Security → Local Intranet → Sites → Advanced and add the WinCC WebNavigator server FQDN to the zone. The WebViewer ActiveX only loads automatically from the Local Intranet or Trusted Sites zones.
4. Open Internet Options → Security → Custom Level and confirm that Download signed ActiveX controls is set to Prompt and that Run ActiveX controls and plug-ins is set to Enable.
5. Open Internet Options → Advanced → Security and confirm that Do not save encrypted pages to disk is unchecked; the WebViewer caches picture data as encrypted blobs and will be unable to reuse them across sessions otherwise.

For Edge IE Mode on Windows 10 22H2 and Windows 11, configure the same Local Intranet zone via edge://flags and the Enterprise Mode Site List. The same ActiveX rules apply.

9. Official Documentation References

• WinCC V7.4: Working with WinCC — WebNavigator (Information System)
• WinCC V7.4 SP1: WebNavigator documentation
• WinCC V7.4: WebNavigator — installation and configuration
• WinCC V7.4: Installation notes and Update 19 readme
• WinCC V7.4: DataMonitor — configuration and operation
• WinCC V7.4: HMI Symbol Library — usage and distribution
• WebNavigator Plugin Builder (WinCC Information System chapter)
• WinCC WebNavigator — operating manual (V7.x generic)

10. Verification Procedure

After the WebConfigurator has been re-run and the clients have been reinstalled, validate the fix end-to-end.

1. On a representative client, open WinCC Viewer RT and connect to the WebNavigator server. Verify that the client installer reports the same build number as the server (read the build from Help → About in both the server project and the client viewer).
2. Load every picture that was previously reported as faulty. Confirm that every Siemens HMI Symbol Library object renders.
3. Open a picture that uses a custom ActiveX control (if applicable). Confirm that the control initialises without an "Object does not support this property or method" dialog.
4. From a Windows command line on the client, run tasklist /m SiemensHmiSymbolLibrary.dll. The output should show WinCCViewerRT.exe as a process that has the library loaded.
5. Restart the client and re-test. A correct fix survives a reboot without re-installation.
6. Open the same picture from a thin-client session via the WebNavigator URL (not the Viewer RT). Confirm the picture is correct in this code path as well.
7. From the Windows event viewer on the client, confirm there are no Application Error or SxS (side-by-side) warnings relating to WebViewer.dll, SiemensHmiSymbolLibrary.dll, or any custom OCX.

11. Field Commissioning Checklist

Use this checklist whenever a WinCC V7.4 WebNavigator deployment is moved, upgraded, or extended.

1. Server and client build numbers match (e.g. both at V7.4 + Upd 19).
2. WebConfigurator re-run after the last server-side update.
3. Project re-published with Web Navigator → Publish.
4. WebNavigator Client uninstalled and reinstalled from the current server installer on every new or changed client.
5. IE cache and %LOCALAPPDATA%\Siemens\WebNavigator cleared on every changed client.
6. Siemens HMI Symbol Library registered on every client (verified by registry key under HKLM\SOFTWARE\WOW6432Node\Siemens\WinCC\WebNavigator).
7. Custom ActiveX controls packaged with the Plugin Builder and re-included in the client installer.
8. Local Intranet zone configured on every client; the WebNavigator server FQDN added to Trusted Sites if it is across a DMZ.
9. First picture load tested on every client from a cold boot; the ActiveX prompt is accepted.
10. Event viewer clean of WebViewer, OCX, and SxS warnings.

12. Troubleshooting Matrix

13. Frequently Asked Questions