I’ve just spent over an hour trying to work out why on my Ubuntu machine, when I wanted to revert from the nvidia-glx-new package (which contains the NVIDIA driver version 9755) to nvidia-glx (which contains version 9631), no matter what I did, it kept loading the 9755 kernel module, breaking Xorg.
Well, it turns out that an empty file called /lib/linux-restricted-modules/.nvidia_new_installed which is used as a toggle for loading the different kernel module versions doesn’t get uninstalled when you remove the nvidia-glx-new package.
Remove the file /lib/linux-restricted-modules/.nvidia_new_installed, and Ubuntu will load the kernel module version 9631 instead of 9755.
