Cannot connect using Windows Messenger
You'll need to check the version of Windows Messenger and make sure you're using 5.0 or later.Earlier versions of Windows Messenger, 4.7 or earlier, are not fully compliant with SIP and may not work well with Brekeke SIP Server.
Note: Windows Messenger 4.7 is pre-installed with Windows XP. Download Windows Messenger 5.0 or later from Microsoft's website.