nvcuvenc Cuda encoder example doesn't work...

Hi guys:

The “CUDA Video Encode (C Library) API” example on http://docs.nvidia.com/cuda/cuda-samples/ doesn’t work, the output .264 file is not playable via VLC(tried rename to .h264, tried mp4box).

My computer:
WIndows 8
Geforce GT 650M (Did tried to called API to check capability, returns “s_ok”)

Help please~~~~!

Thanks in advance.