In case if some-one else trapped on this. By default prevhost.exe is running in Low Integrity mode
Here you can check the list of limitations
In short words you are very limited in places where you can write:
- registry : write to and create subkeys under
HKEY_CURRENT_USER\Software\AppDataLow
- filesystem : write and create subfolders under
%USER PROFILE%\AppData\LocalLow
Also there are limitations on available ways of IPC.