We are using 1.9.8 and have had no problem until today.

Today in our Quizzes, student attempts are being graded, and a score is being given, but in the columns of individual questions, there are no results listed.  Each individual question shows as -/1, instead of our usual 1/1 for a correct answer.

However, the overall score of the quiz for each student is correct in that column.  When I click on an individual question (-/1), I get a "parameter is missing" error message.

Even quizzes that previously in the year displayed correctly now have this problem.

This just occurred for the first time today; all previous quizzes functioned without a problem; what has happened overnight that caused this problem?