SCardTransmit returns error 0x000005aa

I am trying to connect and send command to smart Card through Windows smart Card api , below is the code i have from MSDN. Here the SCardTransmit function always Returns me 0x000005aa , can some one let me know what i am doing wrong.

int _tmain(int argc, _TCHAR* argv[])
{
SCARDCONTEXT    hContext;
LONG            lReturn;
SCARDHANDLE     hCardHandle;
DWORD           dwAP;
const DWORD BUF_LEN = 512;
DWORD dwRecv;
BYTE pbRecv[BUF_LEN];

BYTE sendCommand[]={0x00,0x0A4,0x00,0x00,0x02,0x3F,0x00};

lReturn = SCardEstablishContext(SCARD_SCOPE_USER, NULL,NULL,&hContext);
if ( SCARD_S_SUCCESS != lReturn )
{
    printf("Failed SCardEstablishContext\n");
    SCardReleaseContext(hContext);
    return 0;
}

lReturn = SCardConnect( hContext, "OMNIKEY CardMan 3x21 0",
    SCARD_SHARE_SHARED, SCARD_PROTOCOL_T0 | SCARD_PROTOCOL_T1,
    &hCardHandle, &dwAP );
if ( SCARD_S_SUCCESS != lReturn )
{
    printf("Failed SCardConnect\n");
    SCardReleaseContext(hContext);
    return 0;
}

switch ( dwAP )
{
case SCARD_PROTOCOL_T0:
    printf("Active protocol T0\n"); 
    break;

case SCARD_PROTOCOL_T1:
    printf("Active protocol T1\n"); 
    break;

case SCARD_PROTOCOL_UNDEFINED:
default:
    printf("Active protocol unnegotiated or unknown\n"); 
    break;
}

lReturn = SCardTransmit(hCardHandle,SCARD_PCI_T0,sendCommand,7,
    NULL,pbRecv,&dwRecv );
if ( SCARD_S_SUCCESS != lReturn )
{
    printf("Failed SCardTransmit\n");   
}
lReturn = SCardReleaseContext(hContext);
return 0;
 }

As suggested in comments by Retired Ninja. the variable dwRecv needs to initialize, after initializing the variable the program works. thanks.