I know this is a somewhat old post, but I hope it helps someone else who comes across the same corrupted-backup issue.
I work for a copy that does a lot of iPhone/iPad backup work, and in the process, I've emailed with a lot of people who have gotten the iTunes corrupted backup error. I've been experimenting with repairing the corrupted backups, so that they are restorable again.
We released a program, Decipher Backup Repair, that will fix the errors in an iTunes backup so that you can restore your device in iTunes. The free trial of the program will show you all of the errors it found in your backup, and show you how we can repair them.
http://deciphertools.com/decipher-backup-repair.html
(Note: As I mentioned, I work for the company I've discussed above, so I stand to benefit, either financially or otherwise, from the links I'm recommending.)