Did you create the backup using the same iTunes version? Is the backup made using the same iOS version? If you answered yes to both questions, more than likely the backup is indeed corrupted and unrecoverable. You can, however, try rebooting both your iPhone 5C and your computer and then try the restore process again. It may or may not take. If it does not, consider setting up your device as new, getting it like you want it, and then creating another backup. Having said that, did you by chance create an iCloud backup that you can restore?