You have been trying Messenger 2010 recently after downloading and installing the leaked Milestone 2 beta 15.2.2583.119? You might get problems when you want to go back to Messenger 2009.
The problem – compatibility flags
When you use Messenger 2010 for the first time, it seems that your Windows Live ID gets some special flags in your profile data. Even if you remove Windows Live Wave 4 completely, you might see that your contacts cannot send you nudges or files. Instead, they might get the following message: “You cannot send a Nudge to your contact because he or she is using an older version of Messenger” or similar.
A possible solution
Currently, I only know of a solution that might work. There is no guarantee.
Attention: The price is that you lose all local Messenger settings.
- Close all Windows Live programs.
- Right-click your taskbar, and choose Task manager.
- Click any process called msnmsgr.exe, wlcomm.exe, wlmail.exe, sync.exe, writer.exe, and End process.
- Download and run the tool ZapMessenger by MVP Jonathan Kay.
- Retry to install Windows Live 2009 from download.live.com.
Update: The problem was server-side and has now been fixed. Thanks for your patience!