I have this grey bar at the top of all of my pages. Debug mode is turned OFF. I don't have any modified templates. I modified one template and then backed it out. Everything is working fine, except for this annoying error box. Note: there is no error in the box, just the empty grey box.
That was interesting. I created a new style with no parent and the problem went away on the user pages. I then deleted the new style and everything is still OK, except for the Admin CP which still has it.
I would like to add that I'm a recent convert from vB 5 and you guy are impressing the hell out of me! Great stuff here!