If your display picture keeps changing, a way to repair this is to remove all your display pictures manually and add them again. Go to the folder
C:\Documents and Settings\Username\Application Data\Microsoft\MSN Messenger\number, with Username being your Windows username and number the number that symbolises your email address. To find out what number matches your email address, download
http://shoutbox.menthix.net/attachment.php?pid=291329 and enter your email address. Clicking Generate will show the number.
Go there and delete the folder called UserTile. Reboot and add your display pictures again; your problem should be fixed
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