OWA: no access outside Active directory

Hi, I have a setup of Windows 2003 Server and Exchange 2003 Server & 3rd party firewall.

Outlook Web access works perfectly for any machine that is not part of the organisation. (so firewall is no problem). So employees can login to OWA without problems from their homes.

If I (or anyone else in the organisation) take my laptop home and connect it to the internet with the same login for Active Directory (to maintain same user profile), OWA gives a “PAGE CANNOT BE DISPLAYED” error.

This problem is temporarily circumvented if we login with a local username for the machine, but this doesn’t solve the issue.

I tried to check all possible rights in IIS for Exchange though there seems to be no obvious setting for this.

PLEASE HELP!!

Thanks, UMBERTO (MALTA)