OK so Ive messed around with this issue and realized that my facebook app on my tablet needed an updated. Once I did this..candy crush was able to connect properly!!! So try updating your facebook app on your tablet/phone! You're lucky, I still have the same problem :(
If the app is crashing maybe even a simple restart might help you out. If not then close all your other apps and check that your memory isn't full. These have helped me in the past :) Thanks but I tried everything you said and I'm still unable to play. Hope it'll be solved soon.