I have a Small Biz Server 2003 server with Exchange 2003 and OWA enabled. It's been working great for about three months now, but I'm now seeing very strange problems within the OWA session.
Using forms-based authentication, I can access the OWA logon page and sign in just fine. I can click on a message in the Inbox and view it through Reading Pane or by opening the message. But about 40% of the messages display a generic HTTP 404 "Page Not Found" error in the Reading Pane and when fully opening the message.
There's no pattern to which messages work and which don't, and the frequency varies by mailbox. Another user can't view any new messages from the past 7 days, but all his older messages are accessible.
The Outlook 2003 client can access all the mailboxes and doesn't have a problem reading the messages that OWA can't display.
It doesn't appear to be a permissions issue (though I've been known to be wrong :) ), so I don't want to start messing around with permissions until I get a better idea of how it's even possible that seemingly random messages can't be displayed in OWA when IIS is accessing the same folder/share (\\.\BackOfficeServer\domain\MBX) to retrieve the message.