Sorry, but "Question in the title..." RLY? Sorry, but that's pointless. You need to provide exact information - system, footage used, comp settings, trace settings, anything else. You can't expect people to help you without giving them the necessary details.
OK, You are right.
WinXP SP3, 4GB RAM, Core2Duo CPU (parameters below).
1920 x 1080 x 25 fps - both the comp and the footage video.
I want to trace a masked area from a 5 seconds AVC video. the mask's size is 1020 x 880.
Disk cache enabled with 2GB, but AE does not use it, as i see it on the disk.
And these are the Memory & Multiprocessing settings:
Unless pre-composed, AE will ignore your mask. Your Trace settings also suggest that your trace areas will be tiny, which ultimately will simply exhaust the overall number of masks any AE layer can have. or in other words: You may already have 999 masks on your trace layer and the routine simply stops because it can't add more. Anyway, without seeing the footage, this is of course just a guess.
I had a hint of this, but only about 400 masks created. But i try to increase this value.
Ah, that was the problem. Now with 36 masks all the 5 seconds is traced.