If you look on the 2.51 edit download page you will notice at the bottom that Mountain Lion and Mavericks are no longer supported as they were with 2.30. I am in the same predicament (with Mountain Lion) and thus have had to settle for 2.50 firmware but with 2.30 edit. Alas I don't get all the new goodies with 2.50 but at least it works. Maybe L6 will come up with a fix. I can't upgrade past ML as I use PT 10 and am stuck with that until I go for a major system upgrade.