He has .NET Framework 3.5 and he's tried wiping the MWLL folder and redownloading the installer, it still doesn't work.
The message he gets is "MWLL.AutoUpdater.exe has stopped working", and it comes up immedetiately after launching it, whether via the installer "Click here to run AutoUpdater" or launching the actual .exe...
It might just be his computer, cuz there's not much else info to give.
EDIT: as an aside, is there a way to download the mod without the use of the autoupdater?