Windows Movie Maker has stopped working

I've been using the Windows Movie Maker tool in Vista to do some simple video editing, and it's been working beautifully for me.. until recently when it just stopped.

Now when I import any video clip, even ones that worked before, I get:


WMM has compatibility options to disable video filters - I disabled what QuickTime, DivX and Nero installed (three applications that shouldn't cause Windows Movie Maker to break, since they're so commonly used) and that didn't help.

Any ideas?  It went from a useful tool to just completely broken.