I've been working with cloth for sometime now and I have had this problem before, but my usual fixes aren't working this time. When I playback the animation to simulate the cloth, it refuses to simulate. I get a message saying something like:
"Cloth is not solveing because "Run-up" is not supported. Please rewind to the first frame and make sure that your frame incriments are set to one in the playback settings"
Well they are set to one...and I have it set to play every frame. the timeline starts at 0. Animation starts around frame 16 and the cloth is set to start at fram 5. I cant figure this one out... please let me know if there is something I'm missing.