Sounds like possibly a permissions issue. Have you tried repairing permissions?
There's a known bug in the Finder that causes crashes in some applications when the Finder is in certain view modes. This might be related.
I don't recall whether we made progress on working around that bug in the 10.0.1 update or not, but you should install the update anyway.
If you don't mind, please submit a bug report and include a screenshot that shows the Finder. If you want to submit a bug report with an attachment, you can send it to aebugs -a-t adobe -d-o-t com. Bug reports without attachments can go through here.
I tried fixing the permissions, but it doesn't look like that fixes the issue either. I also downloaded every available update for CS5, and still no dice.
I did some more testing, and it looks like the error actually only happens when I view Movies, or open an iPhoto event in the media browser that only has video files. I also found out that this freezing issue with Movies happens not only in After Effects, but in the entire master collection.
Any other ideas on a possible fix?
Also, I'll send a bug report with some screenshots right after this is posted.