If you wish to keep using version 7 you need to upgrade to the latest version 7:
MSN Messenger 7.0.0820 for Windows 98, Windows 2000, Windows Millenium and Windows XP
Rectification: Even tho it says in the system requirements of 7.0.0820 that you can run it on WinXP you are not supposed to do so. WinXP has gotten into the requirements by mistake, this will be fixed. MSN Messenger 7.0.0820 will only run on OS'es pre-Windows XP (with the exception of Win 95, people on that should use MSN Messenger 5.0)..all on WinXP and Vista will have to upgrade to Windows Live Messenger.
Do not use work arounds to keep using old version, in the end they won't sign in at all anymore and you are risking your computer at that. The upgrade is for a reason, read
Microsoft Security Bulletin MS07-054, Vulnerability in MSN Messenger and Windows Live Messenger Could Allow Remote Code Execution (942099)
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