Incorrect banner saying somebody is offline

While I was chatting with a friend last night, a banner at the top of
the message window saying he appeared to be offline came up on two
occasions. The banner remained each time although we were still
chatting. The person I was chatting with didn't get the banner. The
only way to get rid of it was for me to sign out and then in again.

I'm using the latest version of MSN Messenger (v.7.5) with current XP
Home.

Any ideas what could have caused this to happen?

TIA!

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