Resolving Siemens Scout V4.1.5.3 MSXML Error on XP Pro / Win7 VMware Installations

The MSXML error "The parameter is incorrect; null" at Scout launch is a known failure mode of the persistence layer of the Step 7 / SCOUT integrated engineering environment. On a fresh SCOUT 4.1 SP5 HF6 install, the symptom appears immediately at program start instead of the standard project navigation. The error originates from the UESPersi.dat file under the Step 7 user management folder, not from the SCOUT executable, which is why a generic u7wwbfax.exe.config workaround does not resolve the issue.

1. Problem Details

The reported scenario:

• Host operating system: Windows 7 workstation
• Guest VM: Windows XP Professional SP3 (fully patched), running under VMware
• Engineering suite: Step 7 / SCOUT V4.1 SP5 HF6 (fresh install)
• Comparable installation working on three additional physical machines with the same version combination

Symptom: SCOUT starts, the splash panel appears, and the engineering GUI is replaced by an MSXML error dialog reading:

MSXML error.
The parameter is incorrect; null

The dialog blocks further program interaction. Task Manager shows SCOUT.exe remains resident but in a non-functional state, and S7WINBM.EXE or wrkbnch.exe may also remain in memory with a high handle count.

Affected Components and Versions

Hotfix HF6 (4.1.5.3) is the last publicly released patch for SCOUT 4.1; subsequent maintenance was delivered under SCOUT 4.1.5.x hotfix packages and eventually consolidated into SCOUT 4.2 / TIA Portal-based SCOUT TIA. Reference the Siemens SIMOTION SCOUT download & entry list for the canonical release history.

2. Environment-Specific Failure Pattern

Two characteristics are critical to the diagnosis:

1. VMware virtualisation: The same SCOUT + Step 7 version combination works on three physical XP SP3 machines, so the binary set itself is sound. The problem is therefore environmental, not version-related.
2. Fresh install: The error appears on the first SCOUT launch after a clean install, indicating an empty or auto-generated persistence file is the trigger, not a corrupted user project.

The UESPersi.dat file is the U7-User-Management-Client persistence data file. It records workspace state, recent projects, user-mapped drives, and the registration of installed add-ons. When the file is missing or contains zero-byte data, the S7 wrapper attempts to parse it as XML through MSXML and throws XML_E_PARAMERROR (0xC00CE56E), surfaced as "The parameter is incorrect; null".

3. Root Cause Analysis

The root cause is a malformed or empty UESPersi.dat in the Step 7 user-management workbench folder. The default path on Windows XP is:

C:\Program Files\Siemens\Step7\u7umc\data\wrkbnch\UESPersi.dat

On Windows 7 / Win10 32-bit hosts the same path applies; on 64-bit hosts running XP mode, the path is taken literally as written by the 32-bit installer inside the guest. The file is an XML stream consumed by the SIMATIC Manager ("wrkbnch") launcher and inherited by SCOUT. Failure modes that produce the observed MSXML error include:

• File present, size 0 bytes (truncated write during install)
• File present, contains only the XML declaration with no root element
• File present, contains legacy XML from a previous SCOUT major version (incompatible schema)
• File present, contains UTF-16 BOM but the parser is set to UTF-8 (XP default install order)
• File present, ACLs deny the current user read access but allow enumeration; XML loader fails on read

Why u7wwbfax.exe.config did not help: that workaround resolves a separate MSXML problem in the WinCC flexible (HMI) configuration service, where the .NET config redirector needs to be copied into the Step 7 bin directory. It does not influence the U7UMC persistence layer at all.

4. Primary Solution: Remove or Rename UESPersi.dat

The persistence file is regenerated on next launch. The resolution is to delete or move the file so that the U7UMC service rebuilds a valid one.

4.1 Prerequisites

• Local administrator credentials on the XP Pro guest (or, on Win7, UAC elevation)
• SCOUT and SIMATIC Manager fully closed; verify with Task Manager that SCOUT.exe, S7WINBM.EXE, and wrkbnch.exe are not running
• Folder Options > View: enable Show hidden files and folders and uncheck Hide protected operating system files (XP default hides the file)

4.2 Step-by-Step Procedure

1. Close all Siemens engineering applications, including SCOUT, SIMATIC Manager, and any wrkbnch background processes.
2. Open Windows Explorer and navigate to:
   C:\Program Files\Siemens\Step7\u7umc\data\wrkbnch
3. Confirm the existence of UESPersi.dat. Capture the file size for the diagnostic record (right-click > Properties).
4. Rename the file to UESPersi.dat.old rather than deleting it outright. This preserves a forensic copy in case the underlying problem is more severe (e.g., profile corruption on a domain user).
5. (Optional) Capture the install log: locate installscoutlog.txt in the SCOUT install directory or in %TEMP% and archive it. Siemens support routinely requests this file for MSXML error cases.
6. Launch SCOUT via Start > SIMOTION > SCOUT 4.1.5. The launcher regenerates UESPersi.dat.
7. Wait for the project workspace to open. The first launch will rebuild the persistence file and may take 30-60 seconds longer than usual on a VMware guest with low RAM.
8. Verify the new file exists and contains valid XML.

4.3 Verification Commands

Use these one-liners on a command prompt to validate the regeneration:

cd /d "C:\Program Files\Siemens\Step7\u7umc\data\wrkbnch"
dir UESPersi.dat
type UESPersi.dat | findstr /R "<.">nul && echo XML-OK || echo XML-MISSING

A healthy file is a few hundred bytes, contains a single root element such as <S7Workbench> or <U7Persi>, and parses cleanly. The MSXML error will not recur on the same VM after this step.

5. Diagnostic Information to Capture

If the rename does not resolve the problem, escalate with the following artefacts:

6. Alternate Solutions (If Rename Fails)

The following additional steps resolve stubborn cases, especially on VMware guests with shared profiles or snapshot-restore behaviour.

6.1 Re-register MSXML DLLs

regsvr32 /u msxml3.dll
regsvr32   msxml3.dll
regsvr32 /u msxml6.dll
regsvr32   msxml6.dll

Run each command from %SystemRoot%\System32 as administrator, then reboot the guest.

6.2 Reset User Profile Location

If the guest was joined to a Windows domain and the user profile is a roaming profile, the persistence file may be re-injected at logon. Set the following environment variable to a stable local path before launching SCOUT:

setx U7UMC_PROFILE "%USERPROFILE%\Siemens\U7UMC" /M

Delete the file in this new location, then re-launch.

6.3 Exclude Folders from Antivirus / VMware Sync

Some VMware + Windows Defender combinations intercept mid-write on the persistence file when the AV real-time scanner opens it for inspection. Add the Step 7 root and u7umc tree to the AV exclusion list. The official Siemens note for Step 7 / TIA installations is in the Siemens antivirus exclusions for SIMATIC products KB article.

6.4 Rebuild the Wrkbnch Cache

If SCOUT still fails, rebuild the entire workbench:

1. Rename wrkbnch to wrkbnch_backup (Step 7 will recreate it).
2. Delete the registry key HKLM\SOFTWARE\Siemens\AUTSW\S7RK70A if present and orphaned.
3. Re-run the Step 7 setup in Repair mode.
4. Restart, then launch SCOUT.

7. Related Error Variants

8. VMware-Specific Considerations

Windows XP on VMware Workstation / Fusion / Player is an officially supported SCOUT environment, but the following are common pitfalls beyond the persistence file:

• Snapshot discipline: Restore to a snapshot of a known-good install, but do not roll back after SCOUT has populated UESPersi.dat for the first time; this recreates the empty-file state on next launch.
• Linked clones: Each linked clone has its own writable U7UMC folder, but a parent snapshot with a corrupted UESPersi.dat will propagate. Always rename the file in the parent before sealing the snapshot.
• Time drift: Unsynchronised clocks between the host and guest can cause the XML file's date stamp to be in the future, which Step 7 occasionally treats as a parse error. Install VMware Tools and enable time sync.
• RAM allocation: SCOUT + Step 7 + SIMATIC Manager + WinCC flexible can exceed 2 GB of working set. Allocate at least 3 GB to the XP guest.
• 3D graphics: SCOUT does not benefit from VMware 3D acceleration. Disable it to avoid the VMware SVGA II driver corrupting Win32 GDI calls during the splash.

9. Prevention

After a successful fix, harden the environment against recurrence:

1. Export a known-good UESPersi.dat as a template and store it under C:\SCOUT_BACKUP\ for rapid restore.
2. Document the exact install order: Step 7 first, then Step 7 SPx, then SCOUT 4.1, then HFx hotfix. Out-of-order installation is the most common cause of MSXML errors per the SCOUT installation notes.
3. Disable Windows file indexing on the Step 7 install drive to prevent concurrent file open by the indexer during install.
4. Create a VMware snapshot titled "SCOUT clean baseline" after the first successful launch so a corrupted state can be reverted in under 60 seconds.
5. Periodically verify UESPersi.dat size. If it drops below 200 bytes without a SCOUT reinstall, investigate the AV / disk imaging software.

10. Frequently Asked Questions