15240 to 16000/16010 upgrade loops: "Update Manager script file has been updated. Kindly re-invoke the upgrade."

15240 to 16000/16010 upgrade loops: "Update Manager script file has been updated. Kindly re-invoke the upgrade."

Hi,

I can't upgrade ServiceDesk Plus from build 15240 to 16000 or 16010. Every attempt stops at "Validating the given Patch" with:

"Update Manager script file has been updated. Kindly re-invoke the upgrade."

Re-invoking gives the same error every time, indefinitely. Support asked me to post here.

Environment:
- Windows Server 2025 Standard, Hyper-V VM
- Install path: C:\Program Files\ManageEngine\ServiceDesk
- Bundled PostgreSQL 15.14, not FIPS-enabled
- Upgrade history: 15150 to 15200.3 to 15240

End of updatemgrlog0.txt (identical with both the 16000 and 16010 PPMs):

Instalation buildno is : 15240
Is CorrectInstance is calling
Serverstatus is calling 3
buildNumber 15,240
baseBuild 15,200
retValue 1
[com.adventnet.persistence.DefaultPatchValidator] [SEVERE] : Update Manager script file has been updated. Kindly re-invoke the upgrade.

What I've already tried:
1. Verified PPM SHA256 for both 16000 SP-0 and 16010 SP-0 against the published values.
2. Removed a leftover -DSkipForcedBackUp_15200=true flag from bin\scripts\UpdMgr.bat.
3. Manually applied all six *_new files from the PPM (UpdMgr.bat, AdventNetUpdateManagerInstaller.jar, toolkit-commons.jar, mssql-jdbc-12.10.2.jre8.jar, mssql-jdbc_auth-12.10.2.x64.dll, UpdateManager.sh). SHA256 confirmed identical to the PPM contents for both 16000 and 16010. The log confirms the new launcher is in use (build.version=15280, new classpath).
4. Service stopped, bundled PostgreSQL stopped cleanly with pg_ctl, no java.exe/postgres.exe running before each attempt. Also tried after a full reboot with the service disabled.
5. Cleared Patch\tmp before each attempt.
6. Elevated prompt, launching via both bin\UpdateManager.bat and bin\scripts\UpdMgr.bat directly, including re-invoking immediately after the error.
7. Tried -DSkipForcedBackUp_16010=true: same loop.
8. Imported latest.crt: same loop.
9. Added a Microsoft Defender exclusion for the whole ServiceDesk folder: same loop.
10. UpdMgr.bat exits with code 0 (not 7) after the error, so the launcher's file-swap path is never triggered. bin\fileUpdate.bat does not exist.
11. Console shows "WARNING: UpdateManager conf file does not exists" on every launch.

Any help would be highly apprecaited. Logs available on request.

Thanks!