I have also experienced the lockup problem, but found the cause to be getting ahead of the computer. If I enter any comand, be it even a screen pan, if I do not let the unit finish the privious command it will lock up if I get ahead of it.
Just an update - I've flown another 4+ hours with my iFly without a repeat lock-up. I also tried forcing a lock-up by testing Harlan's comment that "getting ahead" of the unit triggers them, but was unable to verify that observation.