This is pretty strange. I've been doing circular symmetry for a long time with good results but something is goofy with my recent 2013 install; it just doesn't work at all. I'm not sure what is up but I've tried a real simple model with a ful wheel disc with only a rotational load and it seems to solve correctly. With a 1/4 section constrained with circular symmetry it doesn't even come close.
I also notice that I can't run both scenerios in one file without resolving every time I switch the configuration.