Error: Unable to Connect Windows Messenger 5.1 or Earlier to a System with Office Live Communications Server
The following error message may be displayed on your screen when you try to connect to a computer that is running Microsoft Office Live Communications Server using your Microsoft Windows Messenger.
407 Proxy Authentication Required
Moreover, when this happens, your connection may fail.
Causes of Error
This error occurs when one of the following conditions is true:
- Basic authentication is not supported by the Microsoft Internet Security and Acceleration (ISA) Server-based proxy computer.
- Your computer is running Windows Messenger version 5.1 or earlier. These Windows Messenger versions do not support proxy authentication through a computer that is based on ISA Server that does not use Basic authentication.
Resolution Method
To resolve this error, you need to configure your ISA Server-based computer to use Basic authentication.
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