Admin menu itself has sort of gone

At about 7 sites, the admin module is working great, and my users love it!! So a BIG THANKS for this awesome work!

But this is my situation at one site:
As user 1, I see the admin menu bar with the default items.

However
* I do not see the admin menu in the list of menu's anymore
* therefore I cannot add/remove items as wanted in the admin menu - bummer
* but also no other user sees any menu items, although I have given them rights to the admin module and some rights to perform some actions. So practically it's not working at all for my users...

How do I get the admin menu back? Already tried disabling & re-enabling the module, to no luck...