The solution

1. Disable the WMI service

   sc config winmgmt start= disabled  (make sure there is a blank between 'start' and 'disabled')

2. Stop the WMI service

   net stop winmgmt

3. Go to %windir%/System32/wbem and rename the repository-folder

   cd C:\WINDOWS\System32\wbem rename Repository Repository-old

4. 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 [2]. 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.
5. Remove the file found in step 4
6. Search the registry on occurences of “VisualSVN” and remove every found item
   I guess especially the key “Autorecover MOFs” in

   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\WBEM\CIMOM

   was an entry which recreated the faulty *.mof all over again.

7. Enabled the WMI service

   sr config winmgmt start= auto

8. Start the VisualSVN-Installation