nvidia-smi show "Product Name: Unknown Error" and cuInit return 100 code (NO_DEVICE)

I have Ubuntu 12.04 and nvidia driver 346.46 installed. I’m trying to use ffmpeg with nvenc, but when i launch it, cuInit return NO_DEVICE ([nvenc @ 0x1e12f80] >> dl_fn->cu_init(0) - failed with error code 0x64). And nvidia-smi out gives me “Product Name: Unknown Error” (but i can get info about gpu temp and memory for example). I don’t know what i should do to resolve this problem.
What should be my start point?