What is his problem, what do his actions mean?

My sons father left when I was pregnant, met someone else and got married, (he is now divorced though because she had an affair and a baby with her lover) he refused to put his name on my sons birth certificate. My son is now 6 and a half. A few months ago I met up with my sons father on a night out and we spent the rest of the night chatting, him asking about our son etc. We seemed to get along fine. We agreed that we can be civil. We are not young. I am 31 and he is 40. I bumped into him again the day just before New Year and he was very inquizitive. My son was with me and he seemed to take an interest. I emailed him at work last week to ask if he would reconsider putting his name on our sons B Cert (in Scotland the father must be present or have a justice of the peace sign a form)? He emailed me back saying he couldnt read my email and gave me his home email to contact him there. I put a friend request on his page in facebook, which he accepted (so everything seems fine, right). I emailed him on his home email re: B Cert, he never answered, so I left it a couple of days, thinking maybe he just doesn't read his emails (even though I could see he was on line). After a couple of days, I sent another, asking if he had a chance to consider it. Still no answer. Tonight, I IM'd him, and instead of answering me, he signed out. I dont get it. Why be all friendly and why give me his home email to get in touch and why add me on facebook and then just blank me. Why not just say no, he does'nt want to. And I thought I was the one with the problem! Lots of thoughts please :-)