Navigation Bar Problem

So I edited a default navigation bar in my forum. Specifically, the No new messages or simply the messages navigation bar. It has this primary and secondary pictures. When I edit or replace the images, I can't save it because it says "You must provide a menu name." But, there's actually a menu name and since it's default, it can't be changed.

Screenshot:

Goto Admin Panel > Display > Under Pictures and Colors > Pics Management

Select Advanced Mode, scroll down and change the images here

Private Messages :

New Private Messages :

Many thanks, Jake Blues! I appreciate the help.