I had the same problem. It turned out that a program was running that prevented nvidia-uvm from unloading.
In order to find out what that program was, I did
#lsof | grep nvidia.uvm (if needed with sudo) and that gave me the hint as to what was using the module. I got that from this answer: http://stackoverflow.com/questions/448999/is-there-a-way-to-figure-out-what-is-using-a-linux-kernel-modulehttps://stackoverflow.com/questions/448999/is-there-a-way-to-figure-out-what-is-using-a-linux-kernel-module
Then I uninstalled that program because I didn't actually need it, and everything was working again. If you do need the program, you can probably just terminate it or kill it for the time being, and then start it again when you're done.