Problem adding one of the Navigation Bar "Buttons"

I decided to change the Navigation bar on my forum to this:
https://help.forumotion.com/t21148-sleeknavigation-buttonsdark-orange

And I edited all of them without a problem except for the PM and New PM buttons. When I go to change them a message pops up that says "You must provide a menu name". I can't edit anything on the page except for the pictures, so I don't know how I can provide a menu name.

Any help would be appreciated.

Display>Pics
Management
Advanced mode
Change the image there.

It worked, thanks!