Windows Live Messenger won't send messages!

I recently downloaded Windows Live Messenger after my older version of Windows Messenger kept having connection problems..
Everything worked perfectly for the first couple of days, but all of a sudden i just can't send messages. i mean, everything's working, i'm logged in, i see other people are online, i receive messages, but i just can't reply. whenever i type anything it gives me the "the following message could not be delivered to all recipients" message.. if i try like a gazillion times, it might sometime let me send one message to certain people, but then go straight back to not doing it.
i tested my connection in the preferences thing and it says everything is fine.

what can i do to fix this problem? receiving messages and not being able to reply to them is very frustrating...