Failed to invoke nvidia-smi

I am using GTX970 with driver 346 on Obuntu 14.04 .
Trying to query utilization with nvidia-smi or NVML api and got just N/A .
Any idea?

Try running as root if you haven’t done so already.
Also make sure that nvidia driver module is loaded in kernel properly (else #modprobe nvidia).

At least these are first things out of top of my head.

It seems that later driver version (>351)solve this problem.
Many thanks !