Vista - Live Messenger Mobile see contacts online but cant have conversati

This was working for almost two years - now - all of the sudden without
changing anything on my phone this is what happens: (Windows Mobile 6.1)
I see a contact online but if I try and have a conversation i can send
messages buy they never get them. The same thing happens on the other end.
They see me and try and send messages but i never get them. This happens for
all contacts. Also, contacts will go offline and but they still appear online
on my phone. if i try and message them then, i immediately get a 'cant start
a conversation' message. I tried switching accounts and re-adding the same
one. Someone tell me they have a solution or at least the same problem so i
know i am not alone in this

thanks in advance for your reply!
Michael