A quick note on selecting "I don't know this person" on Linked in. When you do this, if the inviter receives 3 or so "I don't know this person" clicks, they are suspended or banned.
Even if he invittee then contacts LI and says I was mistaken, I do know the person, LI doesn't care. They will still boot the inviter. Be careful with your clicks. They won't reverse them.