Web Access Outlook unable to get inbox

Scenario: WinNT 4.0 (SP6), Exchange Server 5.5 (SP3), mail accounts accessed via Internet Explorer browser.

Random users are getting the message “Web Access Outlook cannot get your inbox” when access is attempted via the browser. The MS white paper suggestions of spaces in the user names or too-large profiles don’t apply. The mail can be accessed successfully via Outlook 98 with a profile.

If anybody has had this experience, please reply with your solution.