Upload issue using a USB flash pen

Hello,

I'm getting used to the Raspberry Pi(rate)Box (Raspberry B Rev. 2.0 or 2.1)

So as it is, it's everything ok.

Then I tried to use an USB flash drive. After having browsed this forum, I made the following changes.

In /opt/piratebox/share:

mv /opt/piratebox/share/Shared /opt/piratebox/share/Shared_old
ln -s /mnt/usb /opt/piratebox/share/Shared

The USB is mounted at boot since in /etc/fstab I added the following line:

/dev/sda1 /mnt/usb vfat user 0 0

And it's working fine except for the upload: it allows me to choose a file and, apparently, it is showing the upload process, but it is declaring that "There has been a problem".

I checked that in /opt/piratebox/conf/piratebox.conf

UPLOADFOLDER="$SHARE_FOLDER/Shared"

and in /etc/minidlna.conf

media_dir=/opt/piratebox/share/Shared

Since these variables point to the correct items, which may be the problem? Perhaps a permission problem? I don't believe so:

[root@alarmpi ~]# ls -l /mnt/
total 16
drwxr-xr-x 7 root root 16384 Dec 31  1969 usb

[root@alarmpi ~]# ls -l /opt/piratebox/share/
total 16
lrwxrwxrwx  1 root   root       9 Oct  8 08:23 Shared -> /mnt/usb/
drwxr-xr-x  2 nobody nogroup 4096 Oct  8 08:07 Shared_old
drwxr-xr-x 11 nobody nogroup 4096 Oct  8 06:49 board
-rw-rw-rw-  1 root   root      13 Oct  8 09:45 timesave_file
drwxr-xr-x  2 nobody nogroup 4096 Jun  5 06:34 tmp

At the moment I have no useful ideas...