When you attempt to configure Windows Messenger 5.0 to connect to an HTTP Proxy server that requires user authentication, you are unsuccessful. The User ID box and the Password box on the Connection tab in the Windows Messenger Options dialog box are dimmed.
This problem only affects connections to the Microsoft .NET Passport service. It does not affect connections SIP servers, such as Microsoft Office Live Communications Server 2003, or connections to Microsoft Exchange 2000 Instant Messaging Service.
To resolve this problem, install the latest version of Windows Messenger 5.0.