Exchange Server 2003 OWA Integrated Authentication

We have started having problems with our Exchange Server authentication (after no apparent changes to our exchange server!) Whereas before the Integrated Authentication worked absolutely fine, users now have to enter their username and password again before they can view OWA internally.

I have managed to get this to an acceptable level whereby they do not have to prefix their username with the domain name, but is it possible to regain the old functionality - whereby it would use the Windows logon credentials to authenticate? What could have caused this? I've played with the Authentication settings to no avail...

Thanks in advance!

Interesting. I've never had it not ask to authenticate when logged into our domain then accessing OWA.

Have the setting in Internet Explorer been changed? In the Local Intranet Security settings make sure that User Authentication>Logon is set to "Automatic logon with current user name and password".