Grade changes with auto grader If I use an auto-grading script and allow students to see their would-be grade based on the auto-grader, is it wrong to change their grades after the due date if I decide to change the auto-grader? I'm curious what others think because on the one hand students could go back and change their submissions as many times as they liked prior to the deadline, and many students took advantage of this to do as well as possible. Now that I've changed the script many students now have a zero (including a few who previously scored perfectly). On the other hand, the issue that these students had was a result of not following an instruction I gave out, which I overlooked while writing the original auto-grader. So is it wrong to change the grades or am I justified?
If any student feels disadvantaged by this, then you will have an uproar and complaints to administration. You describe a system in which they depended on the actual thing you built not some "instruction" you gave. 

I would guess that you are stuck with the thing for this group of students, both practically and ethically. Otherwise grading will seem chaotic and unfair to them. Your reputation might suffer both with them and with your boss. 

This sounds more to me like a case of releasing untested or insufficiently tested software. 

One way out would be to void the results of the autogravder for anyone disadvantaged and give them one additional attempt to submit. But that could also be a problem because of time constraints on other things in your course and in their other courses. 

Live and learn. But first, be fair.