Mail stays in Outbox Outlook2003, Outlook2000 OK

[dclarknapm5]

Mail stays in Outbox using Outlook2003 but the same user
using Outlook2000 before the upgrade had no problems. If
any user logs in to Outlook2000 its ok, but any user on
Outlook2003 has this problem. The mail will stay in
Outbox until we delete it or open and resend it from
Outlook2000.

We are connected on LAN to one Exchange 2000 server. I
think the security settings are standard.

Any ideas?

Dare.