Hello everyone , I have problem to software

when I was runnig program ARCS exe code or ARCS source code (it dosen't matter)

I saw this error "Exception in thread Thread-1:

Traceback (most recent call last):

File "lib\threading.py", line 917, in _bootstrap_inner

File "lib\threading.py", line 865, in run

File "ARCS.py", line 5535, in monitorEnc

File "ARCS.py", line 4531, in getRobotPosition

NameError: name 'ser' is not defined"

please guys I need to help thank you.