I have created a k2 menu item of type Categories.
When i access this menu item from frontend i get the error message 403 - ALERTNOTAUTH

All k2 categories are set to public. So is the menu item.

Why is this, and most important, how to fix it ?

I have tried all the things i could find regarding this topic, but nothing helped.
So i figured i might try an install k2 all over again and that did the trick. It all workes fine now, i am allowed to access the menu items.