Hmmm, my understanding of how those throttles work is they are a 3 wire connection.
+5v, Gnd and Data. The data signal will be a value from 0v to 5v that varies to determine throttle position. Inside the throttle is a potentiometer which is essentially a variable resistive voltage divider that will ensure a linear progression from 0v to 5v as the throttle is pressed. (My assumption is linear but not all potentiometers are linear)
If my above statement is correct (and someone familiar with the NCM throttle can confirm its not an on/off style?) then what could be happening is the voltage divider could have lost its ground, in that scenario it'll still "function" as a throttle but the lack of ground is a detectable state by the controller. The throttle if the ground is lost would NOT function as smoothly as it should but I find the NCM throttle is not suited to feathering anyway and functions more like an ON/OFF style throttle.
Other ideas are the potentiometer inside the throttle isn't returning to the fully OFF position when it's not being pressed. The controller would see that as the throttle having being pressed slightly but not enough to actually engage the motor, maybe that causes an Error 2 when the unit is turned on and it detects the throttle slightly pressed?