My guess is that you downloaded calibre on Friday or Saturday morning. A bug was introduced in calibre 0.9.29 that broke CC connections. That bug has been fixed and a new version of calibre was put online on Saturday.
Re-download and re-install calibre. The problem should go away. It has for other people.
See
this post for more information.
Edit: same information as DoctorOhh supplied. Sorry about the overlap.