To check who have blocked you out, enter here:
http://www.checkmsnstatus.com/msn-block-status.html
You then enter the e-mail of the one you want to check and click Check block, altough is showed a window to make a survey, the transparency over the background allows you to see if you have been blocked or not.

What julio.bedoya says is right, never enter your MSN password, the service I posted doesn't need your password because don't need to enter your account to see if you have blocked, because what it tells you is if he or she is online or not, so if he or she is online and it appear a your MSN offline that means you have been blocked of the list of that contact.

May be with an other program called Amsn. This soft by default says who has deleted you.

Tal vez con el Amsn, que por defecto te dice quien te elimino.