First, thanks for your help! Because I've read some horror stories about firmware update and Japanese after taht, I've waited until today to do it...
Yesterday I have tried to reboot the NAS and the workstation to solve the problem - no help. After this night where both were down I can logon to the NAS web administration as if there were no problem at any time. What's that?
Again, thanks for your help. But - never change a running system.^^
Regards