First Thing to say,
Second MSN had a few Problems with its servers.
i mean dude it runs over 250,000,000 People Daily
Re-Add the Person it might have been a server re-start or maintaince so thats what might have been causeing the problem.
Thats not a Virus.
If it was then it would show
Download AVG. and test it.
Hope i helped you bud.