All my contacts is blocked on the skype (I am using msn before) and I can't unblock them. I contacted skype, and they asked me to ask microsoft since the contacts belongs here. And then microsoft customer service asked me to post here. I have found an old post of similar issue, and they said we should do the following:
go to http://people.live.com/ , click on Manage, select Limited Access and remove the contacts from the limited access list.

But for my case, I did the same thing but there is no contact in my  Limited Access!

So I am not sure what to do next~~

Please help~