Windows 8.1 64 bit
NVIDIA GeForce GTX Titan x 3 (SLI is disabled)
NVIDIA Driver 335.23 (latest as of this post)

Blender 2.70 64 bit (Also experienced on 2.69 64bit)

Blender fails Cycles render on 3 GPU systems when Multiple Importance Sampling is enabled in World settings after a previous render with this setting disabled (default). Others also seeing the issue in this thread appear to indicate the issue is independent of OS, video driver version, and Blender version.

Issue reproduction steps:

1. Open Blender 2.70 default scene
2. Switch to Cycles render engine
3. Switch from CPU to GPU Compute in Scene Render settings
4. Press Shift-Z – Render of cube works OK
5. Switch to World settings and check Multiple Importance Sampling under Settings
6. Press Shift-Z, render fails with the following Console output:

CUDA error: Launch failed incuCtxSynchronize()
Refer to the Cycles GPU rendering documentation for possible solutions:
http://wiki.blender.org/index.php/Do.../GPU_Rendering
CUDA error: Launch failed incuMemcpyDtoH((uchar*)mem.data_pointer + offset,(CUdeviceptr)((uchar*)mem.device_pointer + offset), size)
CUDA error: Launch failed incuMemFree(cuda_device_ptr(mem.device_pointer))
CUDA error: Launch failed incuMemFree(cuda_device_ptr(mem.device_pointer))
CUDA error: Launch failed incuMemAlloc(&device_pointer, size)
CUDA error: Launch failed incuModuleGetGlobal(&cumem, &cubytes, cuModule, name)
CUDA error: Launch failed incuMemcpyHtoD(cumem, (void*)&ptr, cubytes)
CUDA error: Launch failed incuMemAlloc(&device_pointer, size)
CUDA error: Launch failed incuModuleGetGlobal(&cumem, &cubytes, cuModule, name)
CUDA error: Launch failed incuMemcpyHtoD(cumem, (void*)&ptr, cubytes)
CUDA error: Launch failed incuMemAlloc(&device_pointer, size)
CUDA error: Launch failed incuModuleGetGlobal(&cumem, &cubytes, cuModule, name)
CUDA error: Launch failed incuMemcpyHtoD(cumem, (void*)&ptr, cubytes)
CUDA error: Launch failed incuMemAlloc(&device_pointer, size)
CUDA error: Launch failed incuModuleGetGlobal(&cumem, &cubytes, cuModule, name)
CUDA error: Launch failed incuMemcpyHtoD(cumem, (void*)&ptr, cubytes)
CUDA error: Launch failed incuMemAlloc(&device_pointer, size)
CUDA error: Launch failed incuModuleGetGlobal(&cumem, &cubytes, cuModule, name)
CUDA error: Launch failed incuMemcpyHtoD(cumem, (void*)&ptr, cubytes)
CUDA error: Launch failed incuModuleGetGlobal(&mem, &bytes, cuModule, name)
CUDA error: Launch failed incuMemcpyHtoD(mem, host, size)

When swapping steps 5 and 4 above to perform first render with MIS World setting enabled, render completes without issue. If Blender is configured to utilize less than three video cards (e.g. 1 or 2), the render completes without issue..