DE2 cannot open a file in the SD card

The function alt_up_sd_card_find_first works perfectly, which can help me print out all the file names in the SD card. (So I think it's not any formatting and size problem of the SD card. It's 2GB and FAT16 anyways.)

But when I call alt_up_sd_card_fopen, it returns me -1, so I can't open, create, and write a file.

Below is my simple code of creating a text file, and print out all the file names:

alt_up_sd_card_dev *device_reference = NULL;

int connected = 0;

char* fileName;

device_reference = alt_up_sd_card_open_dev(SD_CARD_NAME);

short int handler;

char buffer[10000] = "Testing Testing\0";

int index = 0;

if (device_reference != NULL) {

handler = alt_up_sd_card_fopen("test2.txt", false);

if (handler >= 0){

while (buffer[index] != '\0'){

alt_up_sd_card_write(handler, buffer[index]); index++;}

alt_up_sd_card_fclose(handler);

}

else printf("cannot open file: %d\n",handler);

while (1) {

if ((connected == 0) && (alt_up_sd_card_is_Present())) {

printf("Card connected. \n");

printf("fat16: %d",alt_up_sd_card_is_FAT16());

if (alt_up_sd_card_is_FAT16()) {

printf("FAT16 file system detected. \n");

if(alt_up_sd_card_find_first("",fileName)==0){

printf("Files detected: \n");

do{

printf("%s \n",fileName);

}while(alt_up_sd_card_find_next(fileName)==0);

}

else if (alt_up_sd_card_find_first("",fileName)== -1)

printf("No files. \n");

} else {

printf("Unknown file system. \n");

}

connected = 1;

} else if ((connected == 1) && (alt_up_sd_card_is_Present()

== false)) {

printf("Card disconnected. \n");

connected = 0;

}

}

}

I found a similar thread about this issue.

http://www.alteraforum.com/forum/showthread.php?t=34101

But I had the interface already... I don't know why it's still nothing changes???

Please help, thanks