no access after restart of domain server

[toschkoff]

Hello,
i have a QNAP 809U and it is joined to our AD (Server 2003). Connecting to the shares with a domain username works fine. After a while (some weeks), this suddenly does not work anymore. If I join again via the qnap 809u web interface, it works again.

I am not sure but it seems to happen when i restart our domain server - but not always.

Is there a solution to this? We use then qnap primarily for backup and when this happen, our backup program cannot connect to the share anymore and the backup fails...

Thank You,
Peter