Sorry to bump this old topic.
If you're still having this problem (or anyone else who hasn't figured this out yet) you basically need to run catalyst as root. There are a couple of ways I found out how to do this on a few distros I have used. For Mint 11 there should be a "Catalyst (Administrator)" in the launch menu. If you don't have that or it doesn't work you can copy "Catalyst" to your desktop and right click it and run as administrator.
A better (and probably easier solution) is if you're using KDE you simply type the following in the terminal:
That should ask for your root password then opens up the Catalyst Control Center. I believe there is a similar command for Gnome and possibly other DE's you just need to do a quick google search to find them.
A last solution I just thought of and, as such, have not tried is to log out and in the log in screen to simply use "root" as the username along with your root password. Then after that open up Catalyst and change the settings then restart.