Are you sure you played back the movie from the LW dwnld folder & not the Preview file? Everytime yo preview a file, LW creates a preview file. It generally is stored i the incomplete folder & starts with the prefix Preview.

Have you tried viewing it with another player? eg: VLC (has built in codecs) or MPlayer And also ensure you have the latest codecs for QT such as DivX, XviD, 3ivx , etc.

I must confess I think your problem happened to me once but I can't remember what I did. lol