Running Tesla K40 in NVENC SDK 5.0 limited to 2 multiple encoding sessions?

When i try to run more than 2 encoding sessions, Nvtranscoder give me:
NvTranscoder: …/common/src/NvHWEncoder.cpp:447: NVENCSTATUS CNvHWEncoder::NvEncOpenEncodeSessionEx(void*, NV_ENC_DEVICE_TYPE): Assertion `0’ failed.
Anyone have ideas what is going on? NVENC SDK 4,0 have no such issue when running multiple encoding in Tesla k40c

Found the return error from NvEncOpenEncodeSessionEx: NV_ENC_ERR_OUT_OF_MEMORY.

How were you launching 2 sessions. for me, it is getting serialized.