Binary classification but request 3 classes

Hello. I am trying to follow the pytorch tutorial for image classification.
I am using the below link.

I only changed my folder which still same binary and it should be classess number is 2.
However it requires class number is 3.
Does anyone know why and how can I fix it?
I only change the folder of images and do not change other things
Thank you.

Dong Ho Kang

Interesting, can you post the stack trace of your error?

Well Not the error is gone after I reboot the computer.
I cannot reproduce the error.
Does anyone have this experience?
It is really really weird.