I use Indesign CC on a mac at work and I run into this issue at least once a week. I was restarting Indesign every time it happened, but after reading this feed I tried what Craig Yeun mentioned above, but instead of starting a new file, I just copied and pasted in the same indesign file and it magically started working again! Much easier fix than restarting the program. I’ve yet to try it again so hopefully it wasn’t just a fluke thing. :)