I has a problem with driver 275.09.07 on x86_64 machine, <Quadro FX 880M>.
There is errors in X.Org like
(WW) Warning, couldn't open module nvidia
(II) UnloadModule: "nvidia"
(EE) Failed to load module "nvidia" (module does not exist, 0)
But kldstat shows nvidia.ko (system rebooted after driver upgrade)
I didn't observe this problem with driver from ports (nvidia-driver-270.41.19) and any other early drivers.
If it's my mistake please give correct direction.