I should also have said that I am logged in as the admin user (the only user that exists so far) when attempting to do this. I tried creating another user in 2.2 just-in-case and saw the exact same behavior.
Is there an alternate direct URL that I could use to try and get access to the groups management page?
I did try (in 2.2) just to copy over the "groups" files into the "banners" files and was at least able to display something that looked like group management when I selected the admin | system | banners section. This wasn't a workable solution but indicated that this might be a problem with the main.php link matrix (I couldn't figure out the problem though).
If there's anything I can do to test further, let me know. There's nothing generated when I turn on debugging...
Mark