I am seeing a crash when trying to cast a large amount of rays using the RTP_CONTEXT_TYPE_CPU. I am able to reproduce the crash with the unmodified primeSimple example and the command line argument -w 25000 (both the precompiled version and a version built locally). The example does not crash if I use -c cuda nor does my application crash if use RTP_CONTEXT_TYPE_CUDA. The debugger just reports an unhandled exception (access violation) in an optix_prime.1.dll thread.
My computer has 32 GB of RAM with a K4200 and a K5000. My driver version is 364.51. I am using CUDA 7.5. I have tried building against both Optix 3.9 and Optix 4.0 beta.
Please let me know if more information is needed.