SQL error when deleting quiz

When deleting a quiz I got this error:

user warning: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'AND question.status = 1 ORDER BY weight' at line 7 query: SELECT DISTINCT question.nid, question.vid, question.type, nr.title, nr.body, nr.format, qnr.question_status, qnr.weight FROM node question INNER JOIN node_revisions nr ON question.nid = nr.nid LEFT JOIN quiz_node_relationship qnr ON nr.vid = qnr.child_vid AND qnr.parent_vid = 1811 AND qnr.question_status != 2 WHERE question.type IN ( 'long_answer','matching','multichoice','quiz_directions','scale','short_answer','truefalse' ) AND qnr.parent_vid = 1811 AND qnr.parent_nid = AND question.status = 1 ORDER BY weight in /Applications/MAMP/htdocs/drupal-6.13/sites/all/modules/quiz/quiz.module on line 2425.

It looks like the problem is in this section:

if (!is_null($quiz_vid)) {
$where_add[] = 'qnr.parent_vid = '. (int) $quiz_vid;
$where_add[] = 'qnr.parent_nid = '. $quiz->nid;
}

and that $quiz->nid is empty. This could be do to this line not loading correctly,

$quiz = node_load((int) arg(1));

I have to run now and can't debug it at the moment, but thought I should at least report it.