course/quiz problem

i created a course and they have to answer the questions right. if they do answer it right and click "finish lection" they get an error: they are not allowed to finish it. if they click on the right side to the next lection, it works.
My settings where, that they can only pass the quiz and go to the next lection if they pass the quiz, but a lot of people pass it and cant go further. even after Strg+F5. whats the issue, how can i change it? or is it a bug? in this case, please fix it.