That was the right way to fix the HTML. Sorry I got it wrong. Well done for finding the other forum thread.
What you need to do now is to look at those problem attempts, and try to work out if they have any value. Try this query: http://docs.moodle.org/dev/Question_database_structure#Following_what_happens_when_questions_are_attempted edited to have a sutitable WHERE clause. For example
WHERE quiza.uniqueid = {attempt value from the other query}
If you do that, or just find quiz_attempts.id for quiz_attempts.uniqueid matching one of the problem attempt numbers, then you can got to .../mod/quiz/review.php?attempt={quiz_attempts.id} in your Moodle 1.9 site to see what that quiz attempt is.
If you are lucky, you will find all those attempts are reall old, no longer need to be kept, and you can just delete them using the Moodle quiz reports.
If you find those attempts are still relevant, then you may need to try to sort out the data manually in your database before you upgrade. If that is necessary, and if you can give us more information about what the data looks like, then we may be able to help you sort it out.