FSM's usually don't have error states, you tend to crash them first.

Though that is preventable, mostly because the code you run is inbetween transitions and that will return very nice stack traces.

Otherwise, you don't need a trace of a state machine, the state you're in and the current transition should tell you exactly where it's breaking.

If it doesn't, chances are you're breaking state machine definitions by storing wildly complex state outside the machine.