Trashing preferences might help. The easiest way is to use something like this free utility from Digital Rebellion:
[
www.digitalrebellion.com]
While you are there take a look at some of the other handy stuff they offer.
If that doesn't help it could mean that you have a shot on your timeline that for a number of reasons won't render properly. Try the "half off" method. Select just the first half of your timeline and try and render. If it will let you, great the problem is in the back half. Select half of the back half and try again. With a few repetitions of this you will narrow down the part of the timeline that is killing you.
It might be a still that is CYMK or too large. I have had problem with AE rendered outs that were not compatible or other things along those lines.
Good luck
-Vance