Messenger initially works, then doesn't

Both my machine and the machine I am connecting to run XP
with MSN messenger 6.0 and Windows messenger 4.7. When
first sending a message, the messages correctly go
through. After the other user sends me a request for
Remote Assistance, the other computer can only receive my
messages, but messages sent by that machine are not
delivered to my machine, and I do not recieve the
assistance invite.

Any help that can be offered is greatly appreciated.