New image for "you have no new messages" problem

I made my own buttons for forum menu, and replaced the old with the new ones. It all worked perfectly except the "you have no new messages" and its pair "you have new message". When I try to put the link for the new images and save them I get a "You must to provide a menu name" message.
The menu name area is gray and I can's access it.

The same thing happens when I try to just save default forum images - without changing anything.

I was doing this on another forumotion forum without any problem.

I would appreciate it if someone could help me.

Yeah, that always happens, just go to display > pics management > advanced mode, and change it in there.

Such a simple solution
Why haven't I thought of that?

Thank you very much!