Add a line to lang/en/error.php such as:

$string['error_question_answers_missing_in_db'] = 'Unable to import question {$a->filequestionid} into database as {$a->dbquestionid} because answer "{$a->answer}" did not import correctly.';

Being able to tell which question and caused the exception would make it much easier to troubleshoot this problem in the future.

Create a quiz.

Add a multiple choice question with at least two answers.

perform a full backup of the course.

modify the code to get an exception to be thrown.
in backup/moodle2/restore_qtype_plugin.class.php find process_question_answer()
change if ($questioncreated) { to if (false) {
comment out if (!$newitemid)

Restore the backup into a new course. The exception error message should include some debug information.

Finally, revert your code changes and perform another restore. This one should complete without any errors.