SD Card Fat16 not recognized - up sdcard interface

Hi,

when I try to start the university test program in Eclipse, it says that the sdcard is inserted but the File System is unkown. I tried with different sdcards but the problem remains. I tried to debugging and I found where the problem is. Please check the code for the red line. This is the part where the program returns result = false, and I get the message "Unknown File System". I don't really know what I should try now. Any help is appreciated. Thank you in advance. Please aks me if you need further information.

Information SD-Card:

sdcard 256 mb - FAT16 format - tried with 4kb, 8kb, 16kb cluster size

Information about the SoPC:

Avalon_UP_SD_Card_Interface_0 component is connected to:

avalon_slave_0 to cpu.data_master

clock_sink to pll.c0 (pll.co = 50 MHz)

clock_sink_reset to pll.requestreset

conduit_end is wired to nothing

bool Check_for_Master_Boot_Record(void)
// This function reads the first 512 bytes on the SD Card. This data should
// contain the Master Boot Record. If it does, then print
// relevant information and return true. Otherwise, return false. 
{
    bool result = false;
    int index;
    int end, offset, partition_size;
    /* Load the first 512 bytes of data from SD card. */
    if (Read_Sector_Data(0, 0))
    {
        end =  (*((volatile short int *)SD_CARD_BUFFER(device_pointer->base, 0x1fe)));
        // Check if the end of the sector contains an end string 0xaa55.
        if ((end & 0x0000ffff) == 0x0000aa55)
        {
            // Check four partition entries and see if any are valid
            for (index = 0; index < 4; index++)
            {
                int partition_data_offset = (index * 16) + 0x01be;
                char type;
                
                // Read Partition type
                type = (*((volatile unsigned char *)SD_CARD_BUFFER(device_pointer->base, partition_data_offset + 0x04)));
                // Check if this is an FAT parition
                // This is where the program can't find any type of those below
                if ((type == 1) || (type == 4) || (type == 6) || (type == 14))
                {
                    // Get partition offset and size.
                    offset = ((*((unsigned short int *)SD_CARD_BUFFER(device_pointer->base, partition_data_offset + 0x0A))) << 16) | (*((unsigned short int *)SD_CARD_BUFFER(device_pointer->base, partition_data_offset + 0x08)));
                    partition_size = ((*((unsigned short int *)SD_CARD_BUFFER(device_pointer->base, partition_data_offset + 0x0E))) << 16) | (*((unsigned short int *)SD_CARD_BUFFER(device_pointer->base, partition_data_offset + 0x0C)));
                    
                    // Check if the partition is valid
                    if (partition_size > 0)
                    {
                        result = true;
                        fat_partition_size_in_512_byte_sectors = partition_size;
                        fat_partition_offset_in_512_byte_sectors = offset;
                        break;
                    }                
                }
            }
        }
    }
    return result;
}