Hmm I can't tell (Windows Messenger vs MSN Messenger)

This is a complicated issue, and I see you’ve been through this before. What version of Messenger you get depends on what XP you’ve installed, but assuming you mean the last version up-to-date, it is 4.7.3001.

Also importantly, not all 4.7 versions are the same, beginning in 4.7.2005 (there was a .0101 and .0105 too) the authentication method changed which is why the registry key won’t help with these versions. These “newer” versions" will need to be patched to work (Old MSN Support isn’t relevant for them either).

Using a test account, my primary doesn’t have Old MSN Support on.