Did you install version 4191? Did you install the files that NVchooser told you to?
What does find /lib/modules -name nvidia.o -o name NVdriver tell you? If it prints nothing, then you haven't installed the NVIDIA_kernel package. If it prints NVdriver, then you installed 3123 or older -- either upgrade, or try /sbin/modprobe NVdriver instead. Either one should work.
If it prints <some path>/nvidia.o, then you installed the wrong driver. Make sure you use what NVchooser tells you to.