June7: If you read my thread about the ribbon error message you'd know I'm the least qualified person to help. However, one thing I have noticed is that in my testing, if I have one wrong xml line in place, it seems to have adverse affects on what follows. All this seems to be version dependent as well. If you haven't taken the approach to rem out everything in the backstage block, I'd suggest doing that, then testing each addition, one at a time until it goes wrong. At least you might find the offending line. In my case, sometimes it was using "tab" instead of button. It's hard to find reliable info on the idMso names.
Hmm...I think I must've created this post when on page 1.
At least I warned you about my qualifications in this matter.