I haven't found anything on this issue with .wmv files, but it's possible that it was converted or renamed. Just to make sure try converting it to AVI or something (see #2 below)...
Try unchecking boxes in...
Tools, Options, Compatability
until you get it to work. That's the only info I have found so far.
Other suggestions I am reading:
#1 Get
windows media encoder utilities and use the media file editor to reindex the file and try to import it again.
#2 Is it a Divx file (or some other encoding like MPEG) rather than a .wmv perhaps? Divx is not supported in WMM and would need to be converted to an .avi with a standard codec instead, before being used in WMM.
- download
GSPOT (I didn't name it) and use
this guide to determine the codec.