On the attempt to update VisualSVN on my Windows XP I struggled with the following exception quite a long time:
Custom action UninstallWMISchemaExecute failed: Diese Datei ist keine gültige MOF-Datei. (0x8004401e)
I was never faced with WMI before so I started from scratch and choosed to try’n’error. A great help was the artikel found in  and after a while I succeeded—but: I still have no clue why my solution worked, nor could I assure that it is side-effect-free. So use on your own risk!
- Disable the WMI service
sc config winmgmt start= disabled (make sure there is a blank between 'start' and 'disabled')
- Stop the WMI service
net stop winmgmt
- Go to %windir%/System32/wbem and rename the repository-folder
cd C:\WINDOWS\System32\wbem rename Repository Repository-old
- Find the *.mof-file in %windir%/System32/wbem which belongs to VisualSVN
In my case the file was named “6E9A2709F6EB23A5E2F059ACD767AD78.mof”. Inside there were multiple occurences of the string “VisualSVN”—which I found by using Notepad++’s search-in-files-funktionality . Note that the Windows search won’t lead to any useable results since Windows doesn’t do a text-search on *.mof-files by default.
- Remove the file found in step 4
- Search the registry on occurences of “VisualSVN” and remove every found item
I guess especially the key “Autorecover MOFs” in
was an entry which recreated the faulty *.mof all over again.
- Enabled the WMI service
sc config winmgmt start= auto
- Start the VisualSVN-Installation
-  http://blog.technical-life.at/2011/09/nice-to-know-wmi-steuerung-reparieren
-  http://npp-community.tuxfamily.org/documentation/notepad-user-manual/searching/searching-files