MLO: SD card boot failed

Hi,
Am trying to boot through SDcard, in a custom board built by us. the MLO code
is failed at this point
//****************************************************
// initialize file system driver
    if (FileIoInit(&fileio_ops) != FILEIO_STATUS_OK)
    {
        OALMSG(OAL_ERROR, (L"BLSDCardDownload:  fileio init failed\r\n"));
        
        return BL_ERROR;
    }
//*********************************************************

can any one suggest what can be the problem...??

Thanks in Advance.