Opening a corrupted Illustrator .ai file

We have an Illustrator CS2 file, that a co-worker has been working on for the last month, that is now telling us unknown error has occured.

We have tried opening it in Acrobat and saving like we read on the Behance Network, but couldn't get it to work. We can see the thumbnail but when we try opening it, it gets about half way through the Reading Illustrator File and then gives us the error message.

We would really like to get this file open and not loose a months worth of work. Please Help!!