Shoutbox

Well you can only check if the contact is online or offline. and not if he blocked you, also as u can read in the "Block checkers DO NOT work" there is this check box in privacy, it say only contact in my list can see my status and send me messages, if this is checked, wether the contact is online or offline , the block checker will tell he is offline.
so the best way is to check the status at the same time u feel u are blocked not after that, or u have to open a new email, and try to chat with ur contact.
here some blockcheckers : http://blockchecker.msnfanatic.com
http://www.msn-block-checker.com/beta/