Navbar editing problem

Hey, I've had this problem before and somehow my ex co-admin sorted it.
When I'm trying to add new images to the Messages and New messages part of my navbar, it just won't let me and it puts up an error message saying "you must provide a menu name" when there's nowhere to even put one
Help..!?

You have to change that image via the pic management function.
Display>pics management>advanced>general/explore tab