The problem is that there seem to be several ways to install AMD/ATI Radeon Catalyst drivers on Linux Mint:
(1) via the "additional hardware driver" feature
(2) via the Fglrx packages from within the package manager
(3) via the run shell scripts for Linux from the ATI/AMD driver download page.
It seems you can't tell in advance which method works for which version of Linux Mint - you'll have to experiment a bit - or wait for the experience of someone else.
For my graphics card in particular, a VGE 2048MB MSI R6950 Twin Frozer II/OC, I had some success with method (3) for LM 11 and driver versions 11.x (name prefix "ATI"), and for LM 12 and driver version 12.x (name prefix "AMD").
However, at this time it seems we're still getting a BSOD in fglrx when shutting down or rebooting LM 12 - wait and see.
A second BIG problem is that reverting a half-way installation back to VGA sometime leave you with a totally unusable system, if you don't follow the uninstall guide contained in the release notes
. In chapter "Uninstalling the AMD Catalyst Proprietary Driver" it tells you to check your /etc/X11/xorg.conf file, and if possible revert it back to an earlier / original version that is compatible with VGA / VESA mode and operations. If you don't, /etc/X11/xorg.conf may still contain references to the uninstalled fglrx or amdcccle modules, and leave you with an unusable system after reboot.
If you are in that situation already, you need to boot from a Live CD, or mount the failing partition from a still working one, and reset /etc/X11/xorg.conf as explained by the AMD support. Now, in my case again, I didn't have any other versions of that /etc/X11/xorg.conf file available, but I managed to revert back to VGA / VESA with a "dummy default xorg.conf"
. I hope this can help.
A third (little) problem is that the ATI control center (AMDCCCLE) sometimes won't start up, or won't save its settings. If your error message pertains again to the xorg.conf file, then something went wrong during installation of fglrx and it hasn't correctly updated that file. In my case, since I still had a file version from an earlier installation of fglrx, I simply reactivated the earlier xorg.conf file. Another reason could be that the AMD installer couldn't write (or overwrite) xorg.conf for some reason. Try to delete it before launching the installer, and make sure you're running the installer with root authorization.
If AMDCCCLE won't start for other reasons or doesn't save or update its configuration, you may try to start is with sudo from a terminal instead from the user menu.
Hope this helps, let me know;