cudaMemcpy unknown error cudaErrorUnknown returned

I just wondered if anyone has had the cudaErrorUnknown returned from a call to cudaMemcpy.

I know the code works as it is used on a different dataset without problems. I just really need a pointer to where the error might be. My inital thought was error with the cudaMalloc ie. trying to copy back to many bytes, but this seems to be ok.

I had a similar problem.
UnknownError is about wrong pointers. Trying to copy to a location that does not exist. Check the number of bytes that you malloc and try to copy later. Is it the same?