Hi davo,
no, I didn't any backup :( but I's very hard for me to believe there isn't any solution because I can see (via NAS Navigator) that the amount of file (% used) is there but I can't access due to a user doesn't work properly after a procedure described for this case.
Of course, you are right and backup is very important: I learned the lesson... I'll buy a second unit.
Do you think that it could be useful to mount the HDs into a linux system to try to save the data?
Thank you for your support.