I've seen it before, even posted the fix here (it was in the beta forums though, they are now gone)
I only remember it was a mini error, like a file missing or something like that.
I'm on holiday for another week and didnt bring the big laptop where all my installations are. I will only be able to find a solution when I'm back.. (could have been a template not reverted, or a
js file not uploaded... or another file not there, but it was something simple)
Actually a missing closing div but it was because of something and I cant remember what it was...
I'll look into it as soon as i'm back...