well you did right on the first thing
the problem generally is a bad estop but there are other things to check
Here are the probable causes for this error code:
a) E-Stop switch may be depressed or defective (already covered)

b) carriage wiring board may be defective (visually check for damage and check all connections)
c) mast cable may be bad (ohm out wires to check for open or short)
d) vehicle manager may be bad (unlikely)