Quizmaker and Moodle

I have uploaded a quiz to Moodle... my students did the quiz but for most of the students they were able to review the quiz but nothing happened when they clicked on the button to close the quiz. The results don't show up in the gradebook. However, it worked fine for a few students.

When I look at the gradebook I do see that an attemp was made for the students for which the grades don't show up in the gradebook.

The results in the gradebook are as follows :

- For two students the three quizzes worked fine;

- For three studends only two of the quizzes closed and reported the results correctly.

- Lastly for thirteen students none of the three quizzes workeD.

Getting desperate here : the SAME quiz works fine for some students and not for others.

Thanks in advance

Carole