Nope, it uses the same port as any other website.
Check in your security software (anti-virus, firewall, ...) if the sites are blocked or not.
Also check your
HOSTS file if it contains some line which might block websites from Messenger Plus!. Remove such lines if they exist. eg: 127.0.0.1 msgpluslive.net
(note: do not remove "127.0.0.1 localhost")
And in the Internet Explorer settings there are also settings which might block websites. See
here for example (its for version 7, but same applies to other versions).
And check similar settings in your other browser in case you have one.