If you are not running Messenger 2009 yet (14.0.8089.726), you have to upgrade now. The server-side support for Windows Live Messenger 8.5 (2008) has been retired. The next time you sign in, you will get to see a dialog like this one:
What’s new in Windows Live Messenger 2009
Find out on this upgrade details website: http://windowslive.com/Desktop/Messenger/Upgrade.
Updating
Where can I download Messenger 2009?
Go to http://download.live.com/messenger and click the Download button.
But… I don’t want to upgrade :S
Sorry, but from now on there is no other way. I have received very many comments from users that do not like Messenger 2009 very much. My tip: try the new version for once, get to know it, force yourself to try it out for at least 2 days. Then create your objective opinion.
Are my add-ons compatible?
The latest versions of Messenger Plus! Live and MessengerDiscovery are. Download them to be sure.
Possible problems
Here is a summary of the most common error codes and problems you might get.
- Sign-in error 81000306—Proxy settings, Network auto-tuning
- Sign-in error 80072ef3—Corporate firewall, exception list
- Sign-in error 8100030d—Windows Live Contacts cache
- Sign-in error 80048821—Stored sign-in data
- Sign-in error 80048051—Visual themes, Internet Explorer offline mode
- Sign-in error 8e5e0713—Firewall configuration
- Sign-in errors 80072ee2 and 80072efd—Firewall configuration, proxy settings
- More Messenger problems and their solution
The error code you get is not listed? Leave a comment and we will see what we can do. 
More help available
If you need more help, you can get advanced support (for free, of course):
Ask the Windows Live Messenger support team and they will get back to you by e-mail.
Related posts:
- Messenger problems: Resolving sign-in error 80072ef3
- Messenger problems: How to solve error code 8e5e0713
- Messenger problems: Sign-in errors 80072ee2 and 80072efd and their solution
