It sounds like you have cudnn 5 installed. If you’re sure you have cudnn6 on your system:
In a terminal:
echo $LD_LIBRARY_PATH
# should print something like /public/apps/NCCL/2.0.5/lib:/public/apps/cudnn/v6.0/cuda/lib64:/public/apps/cuda/8.0/lib64
export $LD_LIBRARY_PATH=<the string above but without the cudnn5 path>