That has happened to me with my Korgs also many times....I feel its the quick button changes that collide and "cant be processed fast enough" by the operating system that causes the lockups.
Not a good thing while performing. When this occurs You have to fade out gracefully looking like nothing is happening (Smile),... then reboot, and meanwhile turn to a backing track off the laptop while it reboots. The show must go on.
So Dave what next for you, ..