[cifs-protocol] permission denied for cifs mount

[Pierre Frenkiel]

hi everybody
I try to mount an external disk which has a wifi network interface, and
behaves as a cifs server: it fails on my desktop, and works on 2 other
computers. All are running Debian/Wheezy

On 2 laptops, the following command works fine:

  ->mount -t cifs -o guest //wehd/hdd /d6

On my desktop,  where it used to work until last month , I get now:

    mount error(13): Permission denied
    Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)

I'm unable to explain this difference of behaviours.
Can anybody help me?

best regards,