I just found out

I thought I'd share it with everyone. I just converted a video using WinMenc for my M6 and it crashed every time I tried to play it. So I openend it with VirtualDub and cut a bit from the beginning, so that the 1st frame of the video is a Keyframe. The video now plays flawlessly

Somehow the first frame of the Video was a D-Frame (Never heard of that though, but Vdub showed [D] instead of [K] for Keyframe)

nice youve find out il try this with some videos ive could watch