Impossible to deliver a sent messages

Problem description:
When I send an instant message to a contact shortly after I receive the error as in the title
Messenger version:
WLM 8.5 (patched)
Windows version:
Windows XP SP3, I use ProxHTTPSProxyMII v1.5 as suggested

What error are you receiving? Are you able to send a screenshot?

The error message was as in the title, it appeared into the chat window. I think was a remote connection issue of a contact, because I’m able to chat with other contacts normally