Ugh. Okay, thought problem was fixed... it's not. I lock a decent track on track marks on source footage... I apply to a Null that the BG is parented to... when the scrubber lands on the second set of tracker data points (scale/position) the screen goes a deep red. If alpha channel is on, it's a half transparent screen. If scrubber is off data points, screen shows fine.
I ram previewed without BG screen parented to Null, and it plays fine. As soon as I parent BG to Null, or apply tracking data straight to BG image, the problem comes back. I've tried different images with same problem, so it's not just that image.
Without more information, not many thoughts come to mind.
What's your OS and the precise AE version (look in About After Effects)?
What kind of processors and how much memory do you have?
What kind of footage are you tracking? Please specify the codec.
Are you using Open GL?
Are you using multiprocessing?
That ought to get the diagnosis going.
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA