DE2 cannot open a file in the SD card

[Altera_Forum]

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