I have a problem with my samba server

[frédérik toupin]

Hello,

I send you an email for a little problem, I have been having for the past 3 months.I installed windows 7 on some computers and It's seems that everytime somebody closed the computer for a day and more.It seems that it lost he's connection with  the server.
I work on ubuntu 9.04. On samba 3.4. I'm on domain.Everything goes well with the other version of windows even vista but with windows 7. I have the following error :

approbation relation between the domain server and the station has failed .After i cannot log in . Except when I go locally, of course.

Can you please help  me

Frederik