Central Contact List disabled for some Skype for Windows versions
The announcement and more details are here. In short — if you are using any Skype for Windows version between 184.108.40.206 and 220.127.116.11, the Central Contacts List feature is disabled for you. The client continues to work normally, but the contact list will not be synchronised with the contact server. So it’s better that you [upgrade to the latest version](http://www.skype.com/download/skype/windows/) (currently 18.104.22.168) right away. Other platforms are not affected.
We had to make this change because there was a bug in these particular versions which caused the performance of the Central Contact List to be degraded for everyone else. Many users have noted that Central Contact List is not performing reliably at times, and this bug was largely the cause for this. By disabling the Central Contact List for these versions, we make it work better for everyone else.