[Stake Monster]

I've found a solution to play downloaded videos in WMP:

go to:

C:\Documents and Settings\All Users.WINDOWS (or whatever user you use) and rename the DRM folder (it's hidden so you need to enable it) to DRM.old, then create a new DRM folder (make sure to right click it and make it hidden) and try to play the video again.

Basically it renews all your DRM files and that worked for me.