Update your PPC's version of MSN Messenger
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This is a security update for your Pocket PC's version of MSN Messenger, provided by Microsoft.
If you receive this error message ("Logon to the Messenger Service failed because the service is not compatible with this version of the program.") when trying to connect to the MSN Messenger service, then you should install this update.
Be sure to have your Pocket PC connected to your desktop when you run this update!