Error 80 says that the "Range Shift SENSOR is NG, Sensor for range gear shift lever is in trouble," and "contact your local Kubota dealer. The speed range (H, M and L) is not displayed on the LCD screen. The range gear shift lever still works to select the H, M, and L speeds. In selecting M or L, however, the feeling is somewhat different at a start, stop, and other actions."
Shop manual makes the following suggestions: Sensor output terminal is out of adjustment, and Wiring for sensor is disconnected or short circuited, and Sensor failure.
The WSM gives some further diagnostics. Fairly complicated

but not if you are good at computers and electronics. Part can be done using the intellipanel.
The shop manual says to be sure to adjust the mode "k" if replacing the sensor, but it was not immediately obvious to me how to do this. Some of the modes are accessed on the screen on the tractor and some you may need a Kubota laptop. Sorry I can't be of more help, but maybe someone else that has done this will log in.