Shoutbox

After I have blocked and removed a man from my contact list, he/she still
can post me a message, if I still is on-line, but only once. I don't konw why.

If their convo window remains open when you block them, they may be able to send messages using the Offline Messages feature. Once the conversation is closed however, no more messages should get through.

I have already reported this to Windows Live Messenger Team