That's the reason I don't bother with CWM backup/restore and just use Titanium and SMS backup/restore. I think everyone's had the md5 error at some point and it means you can lose quite a bit of stuff!
The problem might just be that you renamed the cwm backup folder when you shouldn't have. If so, you just need to name with to something without spaces in it. Otherwise, the problem is a corrupted backup.