I thought this problem was fixed because I bought a new IMac and haven't had that problem. Unfortunately I am back at school with CC and the problem is back with our computer lab Macs. The XMP preference boxes never worked for me but Becka's suggestion - closing the program and reopening - does work. I will try it with all my students to see if that works for everyone.
I also found out how to get Adobe Encore into CC. You have download Premiere Pro CS6 and Encore comes with it. Then delete PP CS6 but not Encore. Seriously silly to have to go through that but I now have Encore with CC.