This error was coming up on a Backup Exec 12.5 server while trying to do LiveUpdate. Kept giving the error:
Update HOTFIX 160050 failed to install. Review the Backup Exec installation log for more information.
The fix for me was pretty easy. I followed partially the instructions I found here. However, I did NOT reinstall the XML parser.
All I did was re-register the parser dll.
Open the start menu and click RUN. Type “regsvr32 %windir%\system32\msxml3.dll”
and run it… with any luck it should say it was registered successfully. If not then refer to the link for more info.