Welcome to the forums.
You know, I think this happened to me before on my Bionic. I was using Clockwork and the issue was with the way I named my backup file or folder.
Did you manually name your backup file? If so, make sure it has no spaces on the file name. Or just check your back up folder and see if some how the file ended up having spaces on it.
If that doesn't work, I also found this fix. It requires ADB or maybe you can run the commands through Terminal. I am no expert on ADB though. Sorry.