if its not due to having two different verstions of MSN messenger, it may be a connection problem... disabling the "QoS Packet Scheduler" might help
Edit: sorry my directions for that were kinda vague before here i fixed them.
1. go to the Control Pannel
2. Go to your Network Connections
3. Right click connection through which you connect to the Internet
(If you are connected via a router or LAN, this will be the "Local Area Connection")
3. For a "Local Area Connection" make sure you are on the "General" page of the "Properties" configuration.
For all other connections click on the "Networking" tab.
4. Click off the "QoS Packet Scheduler" check.
5. Restart the computer
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