Encoding at 40 fps Using NVIDIA Video Codec SDK

I’m trying to use Nvidia’s sample cuda SDK (version 4, can be found at https://developer.nvidia.com/nvidia-video-codec-sdk) to encode a video at 40 fps. However, when I try to encode the video to be more than 30 fps (at 1080p), the encoder fails to initialize and I get the following output:

GetNumberEncoders() has detected 1 CUDA capable GPU device(s) <<
[ GPU #0 - < Tesla K40c > has Compute SM 3.5, NVENC Available ]

InitCUDA() has detected 1 CUDA capable GPU device(s)<<
[ GPU #0 - < Tesla K40c > has Compute SM 3.5, Available NVENC ]

Select GPU #0 - < Tesla K40c > supports SM 3.5 and NVENC

nvEncoder Error: NVENC H.264 encoder initialization failure! Check input params!

Normally when I run it at 30 fps, the code successfully runs with the following initializations:

GetNumberEncoders() has detected 1 CUDA capable GPU device(s) <<
[ GPU #0 - < Tesla K40c > has Compute SM 3.5, NVENC Available ]

InitCUDA() has detected 1 CUDA capable GPU device(s)<<
[ GPU #0 - < Tesla K40c > has Compute SM 3.5, Available NVENC ]

Select GPU #0 - < Tesla K40c > supports SM 3.5 and NVENC
CNvEncoder::AllocateIOBuffers() = Size (1920x1080 @ 16 frames)
System Memory with 16 buffers.

NVENC Encoder[0] configuration parameters for configuration #0
GPU Device ID = 0
Frames = 0 frames
ConfigFile = (null)
Frame at which 0th configuration will happen = 0
maxWidth,maxHeight = [1920,1080]
Width,Height = [1920,1080]
Video Output Codec = 4 - H.264 Codec
Average Bitrate = 6000000 (bps/sec)
Peak Bitrate = 0 (bps/sec)
Rate Control Mode = 2 - CBR (Constant Bitrate)
Frame Rate (Num/Denom) = (30/1) 30.0000 fps
GOP Length = 30
Set Initial RC QP = 0
Initial RC QP (I,P,B) = I(0), P(0), B(0)
Number of B Frames = 0
Display Aspect Ratio X = 1920
Display Aspect Ratio Y = 1080
Video codec profile = 100
Video codec Level = 40
FieldEncoding = 0
Number slices per Frame = 0
Encoder Preset = 0 - Default Preset
NVENC API Interface = 2 - CUDA

When I ran the program through a debugger, I found that the initialization fails when it executes:

nvStatus = m_pEncodeAPI->nvEncInitializeEncoder(m_hEncoder, &m_stInitEncParams);

I was then unable to go into the nvenc APi.

Is there any setting that I am running incorrectly? I am using a Tesla k40c video card, which should be able to encode 1080p at more than 30 fps.