I have an error code C56 on my kubota m 100 gx. What does that mean

In the manual below under troubleshooting it has error codes but not as you listed it. I will tell you in cars I have removed the negative cable from the battery and left off for 30 minutes and it cleared most codes, it did not work with ABS and Traction control codes.
https://kubota.ca/getmedia/f98e6f6e-386b-4fb6-b78f-963dcc5bad2a/L3560,L4060,L4760,L5060,L5460,L6060-ROPS-OPS-EN-TD35019582?ext=.pdf

Communication failure "CAN bus error"

Tractors are no different than autos now... several computer controlled modules talking. If you stowed it with out cleaning out field trash, check for mice damage.

The code means your EGR valve is overheating. Attached is a link that discusses this and potential fix/solution for you.

Engine Error Code Page 3 OrangeTractorTalks Everything Kubota

Semper Fi,
Z

2nd attempt to answer. EGR valve overheating.
Refer to following link for discussions.

Engine Error Code Page 3 OrangeTractorTalks Everything Kubota

Good luck.
Semper Fi,
Z

This could be a low voltage problem. Check the voltage output with a volt ohm meter at the stator output.

the error code means Communication error between copier and PFC.Check cable from pc to printer.

C56 indicates Communications error between the PFC and the CPU on the main PWA. What u can do:
1.Check if the connector CN36 or CN35 on the relay PWA is disconnected.
2.Check if any conductor pattern (PFRXD, PFREQ, PFACK, MACK/PF, PFTXD, or MREQ/PF
between the IC, IC2 and CN36) on the relay PWA is open- or short-circuited.
3.Replace the relay PWA.
4.Replace the PFC PWA.
5.Replace the main PWA.

C56 is communication error between the PFC and the CPU on the main PWA
Check the connector of the replay PWA, PFC PWA, main PWA

Communication related service call C56-Communication error between PFC and M-CPU

(1) Check the signal patterns (REQ, ACK, RXD, TXD) between IC11 (G/A) and IC21 (PFC) on the
LGC board for open-or short-circuits.
(2) Replace the LGC board.