CUDA PRNG program is not working properly sometimes (cuRand)

I have written a simple pseudo-random number generator using cuRand. After successfully compiling it, I try running the executable but after running several times it works properly and gives me random number.

What am I missing here should I do some initialization for my device in order to make it properly work in first run?

Here is my code :

void initializeCUDA(int argc, char **argv, int &devID, int &iSizeMultiple)
{
// By default, we use device 0, otherwise we override the device ID   based on what is provided at the command line
cudaError_t error;
devID = 0;

if (checkCmdLineFlag(argc, (const char **)argv, "device"))
{
    devID = getCmdLineArgumentInt(argc, (const char **)argv, "device");
    error = cudaSetDevice(devID);

    if (error != cudaSuccess)
    {
        printf("cudaSetDevice returned error code %d, line(%d)\n", error, __LINE__);
        exit(EXIT_FAILURE);
    }
}

// get number of SMs on this GPU
error = cudaGetDevice(&devID);

if (error != cudaSuccess)
{
    printf("cudaGetDevice returned error code %d, line(%d)\n", error, __LINE__);
    exit(EXIT_FAILURE);
}


if (checkCmdLineFlag(argc, (const char **)argv, "sizemult"))
{
    iSizeMultiple = getCmdLineArgumentInt(argc, (const char **)argv, "sizemult");
}

iSizeMultiple = art_min(iSizeMultiple, 10);
iSizeMultiple = art_max(iSizeMultiple, 1);

cudaDeviceProp deviceProp;

cudaGetDeviceProperties(&deviceProp, devID);

checkCudaErrors(cudaGetDeviceProperties(&deviceProp, DEVICE_ID));

DEVICE_ID = devID;
printf("GPU Device %d: \"%s\" with compute capability %d.%d\n\n", devID, deviceProp.name, deviceProp.major, deviceProp.minor);


// use a larger block size for Fermi and above
block_size = (deviceProp.major < 2) ? 16 : 32;
} 

And this is my PRNG code:

checkCudaErrors(cudaMalloc((void **) &d_data, mem_size));
size_t n = size_mat; 
curandGenerator_t gen;
 /* Create pseudo-random number generator */ 
(curandCreateGenerator(&gen, CURAND_RNG_PSEUDO_DEFAULT));
  /* Set seed */
(curandSetPseudoRandomGeneratorSeed(gen, 1234ULL)); 
   /* Generate n floats on device */ 
(curandGenerateUniform(gen, d_data, n));

Thanks in advance.