Revisiting a quiz question to review answers

We want a learner to be able to complete a quiz question and click Next to move to the next slide. We also want the learner to be able to click Previous and return to the quiz to see the answers. Then, click next to continue with the course. At the moment, when revisiting a quiz slide, the NEXT button becomes disabled and the Correct or Incorrect popup box appears.  A colleague sent me a course in which the quiz works as it should. I've compared my selections to the one that works and they are the same, e.g. automatically decide, correct triggers for the layers. I copied the slide that works and copied my question and answers into it and it works fine. What am I missing? Please help.