Shortcode.php error

When I get to the end of my quiz, it says:

Warning: Invalid argument supplied for foreach() in /home/content/20/8858420/html/learnjapanese/wp-content/plugins/wp-survey-and-quiz-tool/lib/Wpsqt/Shortcode.php on line 504

Warning: Invalid argument supplied for foreach() in /home/content/20/8858420/html/learnjapanese/wp-content/plugins/wp-survey-and-quiz-tool/lib/Wpsqt/Shortcode.php on line 504

Warning: Invalid argument supplied for foreach() in /home/content/20/8858420/html/learnjapanese/wp-content/plugins/wp-survey-and-quiz-tool/lib/Wpsqt/Shortcode.php on line 504
Exam Finished

Then it shows a review of the first section. Then:

Section 2
Error – no questions
Quitting.

There are four sections to my quiz so far. What can I do to fix this?

My quiz lives here: http://www.learnjapanesewithme.com/jlpt-n5-practice-test/

http://wordpress.org/extend/plugins/wp-survey-and-quiz-tool/