This sounds like some kind of GPU-related issue. What kind of source content are you using, and what format are you outputting to? Are you using Ray-Traced rendering?
it´s a H.264 Video with 420 pixel format generated by a tool called LRTimelapse (using FFMpeg for rendering).
don´t know about ray-traced rendering, sorry :-)
Although AE should cope fine with H264 video, try converting the source video to an intermediate codec (like Quicktime PNG or Animation) before importing to AE. This will at least eliminate the source footage as the culprit.
Ray-traced rendering is dependent on your GPU, and may have implications if there is something wrong with your display card, drivers, RAM etc. Make sure you are switched to Classic 3D in Composition Settings, if you don't need it to be on.
thanks alot - got it :-)