windows movie maker error

Windows Movie Maker error when importing video files?
The file blah blah cannot be imported because the codec required to play the file is not installed on your computer. If you have already tried to download and install the codec, close and restart Windows Movie Maker, and then try to import the file again. I can play the avi file on real player and in windows media player but it will not import.. Please help.
Get ANY other program to work on your videos. Arcsoft “showbiz”, Ulead Video studio or just about any other program is better than WMM….Movie maker sucks BIG TIME!
Windows Movie Maker Error