Just to put my 2 cents in with a vote for force-quitting Create Disk.
Been driving myself nuts for two days. Whether I am creating a dvd or a disk image, it stalled at 66% "Waiting for Create Disk to complete".
Have been waiting to upgrade to Sierra and the next FCPX update (10.3.1) until I finish this project. Which, of course, would be finished now if I could have burned the dvds already, LOL.
On the other hand, maybe upgrading to Sierra and/or FCPX 10.3.1 would have solved the problem. I'll check that out, too. Of course, since we also all talk about the 100's of dvds we have burned successfully, getting it to work after updates is no sign of a permanent cure...
Like all the rest, have had no problem burning from in FCPX.
Considered dumping my 720 version video file into iDVD, but looks like I'd have had the same problem without feedback on why. May try it anyway, just in case.
Been searching communities all day, and finally asked the right question by quoting "Waiting for Create Disk to complete".
Hooray, and thank you very much for a solution that seems to be working. At least, it did this time on a short test video.
Thanks again, even if it is a stupid half-step that shouldn't be necessary.