One of the computers (MacBook Air) on my network has suddenly stopped allowing other users to connect to it. It appears in finder under SHARED but there is no CONNECT AS option, just SHARE SCREEN. Sharing is enabled and I have checked absolutely everything from what I can find in these and other forums. It used to work fine and now it's suddenly stopped. Although every other machine on the network can see the computer, nothing can connect to it. Any ideas?