Private Messages Image in Navbar

Hi everyone, I'm having a problem replacing the text-only navigation with buttons on my forum. Well, one button in particular, the PM button.

Every time I try to save changes to the Private Messages menu in the Headers & Navigation admin, I get an error message saying "You must provide a menu name". I find that rather odd, mainly because you can't change the name of the menu to begin with. Even if I change nothing, leave it EXACTLY as it was by default, (Clicking on the cog to edit it, then clicking "Save" immediately once I get into the Modify screen), it still gives me the same error.

None of the other Nav menus did this. On the others, everything went exactly as the tut in the FAQ said. I've tried multiple themes and images. By the way, the Basic CSS for my theme is too long to be customized via the admin panel, so any possible fixes through that are not an option. At the moment, I took off all of my buttons so that my users can still get to their PMs while I try to fix this.

Am I missing something?

Add images for those buttons here:
Administration Panel > Display > Colors & Pictures > Pics Management
Advanced Mode
General/Index Tab

Thank you! Thats one problem down, however I still can't save the changes I've made. I still get the same error message.

Hello,

You can only change the navigation bars here, as slg mentioned:

slg wrote:Add images for those buttons here:
Administration Panel > Display > Colors & Pictures > Pics Management
Advanced Mode
General/Index Tab

Oh, I'm sorry, I misunderstood you.

Thank you both for your help.