Are you using MetroNoob's stock cwm backup? If so, redownload it and restore it AS IS (in other words, don't manually delete the
.Android_Secure.TAR file or anything else). After you have restored it successfully, you can wipe data if you like and everything should work just fine.
If you're getting the mismatch on a backup you made yourself, it's possible that the folder containing the backup has had one or more files changed or deleted, in which case there really isn't much else you can do to restore that particular nandroid backup (at least to my knowledge, correct me if I'm wrong

).
Hope this helps