Cannot delete UserGroups

I cannot delete UserGroups... I can add users, change
the name, etc... but not delete...

do I have to do something special to activate it?

You should be able to right-click on it from the tree on Security -> Access Controls, and click "Remove User Group".

I swear it was not working last night when I put it in my list
of things to ask.... now it works fine...

I am having the same problem, but following your instructions does not work. The item is acting like it is grayed out. I have cleared the cache, flushed permissions, flush all sessions, hit the refresh button, but still the remove user group menu item on the right click context menu is acting as though it is grayed out. I even went into the user group and removed all permissions manually and then tried to remove the group but that didn’t work.

Please help.

This was a bug in 2.0.4: https://github.com/modxcms/revolution/commit/029256b0b8685e3fc7c262ea2687c9f8b85054bc