I received the error message "unspecified launch failure" in following part. off_t *matches_position; ...... cudaMalloc ( (void **) &mat_position, sizeof(off_t)*10); ...... cudaMemcpy (mat_position, matches_position, sizeof(off_t)*10, cudaMemcpyHostToDevice ); ...... err=cudaMemcpy (matches_position, mat_position, sizeof(off_t)*10, cudaMemcpyDeviceToHost ); if(err!=cudaSuccess) { printf("\n3 %s\n", cudaGetErrorString(err)); } Do you know why this error message is reported??