Hey, not sure if that's what you mean but I got the same problem recently or at least similar; there was a huge green triangle in the bottom right corner of any video played in most players (except vlc of course, which is the second coming) - it started annoying me for some WMV files which I could only play in WMP.
Decreasing the hardware acceleration slider, pressing apply and then putting it back up all the way was enough to fix the bug !
Hope this helps.