Mac Messenger Problem

Hi there, I'm new to these forums and I have a bit of a problem with Mac Messenger. Basically, I accidently deleted a contact from my messenger list, and even though I've added them again, every time I sign in, it says "so and so has added you to their contact list, do you accept or ignore?"

Every time I accept, yet every time I sign in I'm asked to add them again and again.

What's more, the person can't see me online even when I add them.

Any suggestions?

And now for some reason, whenever someone sends me a message, a message comes up asking if I want to accept...

And I appear offline to all the contacts.