I'm kinda new in After Effects. I was trying to to make the effect from this tutorial http://library.creativecow.net/articles/rabinowitz_aharon/CC_Flashback/video-tutorial wich I think it could be useful for a short film I'm working on. So... i did the whole thing and if I RAM render it looks pretty near; but the trouble comes when I export the video. A white rectangle appears, and as far as my knowledge can say, I think that the effects maybe aren't being exported well.
What render settings do you use? Could be that one of the render overrides comes into play here and stuff is rendered at different quality settings liek without motionb blur or such. Also, since expressions are involved, do not use MP rendering. Some expressions do not give correct results with multiprocessor/ multicore rendering.