The Windows Live Messenger Team notifies Messenger users in a blogpost that the mandatory update for version 8.5, as announced back in August, has begun. Users on Windows XP will need to ensure that they have installed Service Pack 2 (SP2) or higher, otherwise the upgrade will not work.

Incase you have issues or questions during this upgrade process, the team provides the following resources:

• Troubleshooting Login Issues
  This post from the support team provides some guidance into how to determine what error you are getting and steps to resolve many of these.
• Online Help
  You can also try the online help pages.  On the left hand side, you can select ‘Table of Contents’ (near the bottom) and get information on troubleshooting and error codes.
• Contact the Support Team
  If you have already tried the going through the online help suggestions and still having difficulties then you should consider contacting the Messenger support team and providing them with more information about the problems that you are encountering.

Users on Messenger 2009 (version 14) will have to upgrade too starting November 9th, unless they already installed the latest version (Build: 14.0.8089.726).

Wondering which version you have? You can find out by going to Help > About in the menu. Don’t want to wait? Go get the current version from http://download.live.com/messenger