I am having a similar issue to kinetic4307 & Jaiden. I keep trying to open an AE file and once it tries to save it crashes. I even tried reverting to a previous verison of AE with no luck. Im on a mac, and I dont have any plug ins. I also cleared everything, which was the first recco when googling.
Note: I do have 3rd part plugins running but they are not in the common folder mentioned above. I rely heavily on these plugins so removing them isn't an option.
Removing them temporarily for troubleshooting purposes would be helpful. If you remove them and the crashing remains, we know more. If removing them makes the crashing stop, we know even more!
Does it generate any crash report? Try removing the third-party plug-ins?
Go to HD/Library/Application Support/Adobe/Common/Plugins/7.0/MediaCore and move all the files and folders (except dummy.txt) to the desktop and try to launch After Effects.