Missing files in my Ableton projects has been a real pain for me in the past so I wrote this script that will use spotlight to find matches with the same file name and file size and then inject them into a new Ableton set. Saves me a lot of time, I hope it saves some of you time as well. I'm hoping to get some collaboration on it, too.
http://github.com/anthonylauzon/ableton_resurrector
Ableton: what kind of CRC are you using on the project files?