Error updating Potentials Stage Field

I am attempting to delete one of the default set of stage fields - Id. Decision Makers. When I go to Save the changes, I receive the following error: "Please enter valid sort order values", even though I haven't edited the values, and they are already in sequential order. (See attached screenshot.) I tried deleting a different field with the same error... I also tried removing the sort order and leaving it blank, but received a different error that the value could not be blank. Stumped as to how to get around this?