The problem is with question S8C6. There is a select_one named summary but it does not define a choice with value 1. The calculation can result in choices with values 1, 2, 3 or 4. That's why the error says "see if value 1 is a valid option".
I don't know why the question is showing up as null. To troubleshoot this one, I quickly modified the JavaRosa source to add the label text to the error message here. I think this would have been a very difficult one to figure out without the source code.