I found this thread when I searched Google to find out why I couldn’t delete contacts from my block list on MSN. I tried a few of the methods put down here. And this is what I found.
When I went into “Contact list clean-up” (an MSN Plus! feature) I noticed that all of the contacts I have been trying to delete from my block list have still got me on their MSN list, except one. I deleted it and went to my MSN block list to see if I could delete it from there as well and I could.

I hope this was helpful!