It could be that a library or runtime file has been corrupted those are the files that have the extension .dll(dynamic link library) They are the files that after effects will look for and rely on when starting up or when performing a particular task. Its the same with any present day windows based program. Another thing is that there could be an incompatible script or payload on your system conflicting with those that adobe have installed. If you have installed anything on your system in the past few days remove it and do a registry clean.Also if you had a beta version of AE or any other adobe cs3 product on your system or still on your system then their relevant scripts could also be interfering.If the problem is still persisting may i suggest that you run Adobe CS3Clean Script. Once you ahve done that re-install the program. if the problem then still persists contact Adobe Technical Support
I hope this helps you in some way!
Kind Regards,
Jack