When I select the X.org Radeon open source driver, Unity does not load. However, when I select the Proprietary AMD Driver from the official Ubuntu repository, Unity does load. Why is Unity doing this? I had no problems with switching between these drivers in Ubuntu 12.04 LTS. This started happening when I upgraded to Ubuntu 12.10.
Before I ever installed the propriatery AMD driver, the X.org driver loaded Unity fine, but very sluggishly. I downloaded the AMD driver from their official website and installed that first and that is what started this problem. I removed that driver and went back to X.org and X.org didn't load Unity either. Then using Synaptic, I installed the AMD driver from the Ubuntu repositories and thats what I'm using now. I'm very confused why that downloaded AMD driver would effect X.org.
I have a AMD Radeon HD 6620G. It's integrated graphics on my AMD A8-3500M Fusion APU (Accelerated Processing Unit as AMD advertises it). Here is a Wikipedia article on my A8 Fusion APU Here.