I was annoyed when I found out that Ubuntu 11.10 Oneric Ocelot didn't allow installation of Gnome 2, so I decided to get the closest thing that still has support: Mint 12 Lisa's MATE interface. I added Lisa repositories and installed MATE based on the instructions here: http://www.addictivetips.com/ubuntu-linux-tips/install-linux-mint-mate-desktop-in-ubuntu-11-10/.
When it refused to run on my computer, I uninstalled it. But then I realized that my system was confused by the addition of the Lisa repos (it even thinks it is Lisa). Strange glitches started happening, so I removed the repositories. Now I'm finding that when I try to force the versions of packages back to Oneric, Synaptic thinks I'm trying to uninstall them, and keeps recommending packages for i386 (I'm using AMD64).
Does anyone know how to restore my system without re-installing the OS or risking actual damage? Right now most of it works at least well enough for me to tolerate, but some less-important parts are completely unusable.