what changed from messenger 7.5 to 8.0???

I'm sitting behind a (corporate) firewall and messenger 7.5 was running just
fine. But since I upgraded to messenger live several days ago, I consistently
get a "Your display name could not be changed. Please try again later" popup
and my login fails. When I bypass the firewall, logon succedes and so I
assume it's neither a local nor a messenger service problem, but it's a new
requirement for the firewall config?

The Connection TroubleShooter reports everything as working an puts a green
checkmark on everything except wireless (which gets no marking) - that's
currently disabled and so that makes perfect sense.

I get the same (positive) results when I click the test button for the HTTP
connection.

I even created the MsnMsgr.txt logfile - but while it's pretty big, it's
pretty unreadable for me too.

Any suggestions? ideas?