Entourage 2004 disconnects

[Fel]

I have 6 machines running Entourage 2004 with email
accounts on an Exchange 2000 server. 2 of them keep
disconnecting the users after a few minutes, and will not
let them reconnect until the software is restarted. I have
checked all the setting with the other 4 working machines
and everything is similar. I also forced the "send receive
all" task to occur every minute. They still get
disconnected.
Is there a setting I am not seeing that will prevent the
network disconnection to occur? What will make the
software remain connected?

Please Help...

Thank you,
Fel