I'm running an 11.10 system, and for some reason, LightDM always covers my screen with purple blocks without FGLRX installed. There's no problem with starting X, only LightDM. I have reinstalled Ubuntu multiple times from scratch only to have this problem over and over again. Even funnier, everything works like a charm when booting off the LiveCD, but when it's installed, LightDM becomes corrupt.
I tried adding "nomodeset" to GRUB but that ended up with LightDM not loading at all. Please help!