Every now and then, iTunes backups may turn out to be corrupt. Error messages shown in iTunes for a corrupt backup can vary depending on the main issue, sometimes without giving many clues on the real problem.
In most instances, it’s almost impossible to repair corrupt encrypted backups, and certainly not without a full understanding of what is missing and how to fix it. However, if a backup wasn't encrypted, it is generally easier to recover with a partial set of files.
The following messages may indicate that a backup is corrupt:
Error loading backup in ... Not a valid mbdb
Couldn't load backup in /Users/Username/Library/Application Support/MobileSync ... file opened is not a database file
... there was something wrong with the manifest an underlying SQL exception occurred
AuthData Value was not a dictionary/node
Could not determine manifest format
The free edition of iPhone Backup Extractor has a number of backup recovery features which are designed to help with corrupted backups, and our support team may well be able to help, and they can do so if you're able to share copies of your Manifest.plist, Manifest.db, Info.plist and Status.plist files.
We publish a guide for working with corrupt backups, and it describes the main ways of recovering data in detail.