The message simply means that something is already using the HTTPS (443) port on your machine. Now there are two things you should do to fix this and ensure it stays that way. The first thing you need to do is disable HTTPS sniffing.
Open up C&A. Go to Configure -> Filters & Ports and untick the HTTPS box. Press Apply and then OK.
The next thing to do is download something called TCPview. (Click Here) Open it up and this is what you’re looking for.
Now it may not be Skype that’s using the HTTPS port, it could be anything. Just click on the Local Port tab at the top to sort by name and scroll down till you find either HTTPS or 443. End the process and voila. HTTPS is no longer in use and your back on track.