Similar issue.  Built a quiz question with multiple correct answers (click all that apply) using clickboxes and advanced actions. AA on entering slide makes sure everything is reset (hiding and showing buttons, resetting 4 variables to 0).  When you select answers and click Submit, it checks for correctness and displays appropriate feedback.  Clear button goes to next slide, which is a dummy to simply return back to slide and therefore execute the reset code on slide entry.  If you get the question right, Next button jumps two slides ahead for the next content slide.

Everything works perfect first time through, even if learner gets it wrong multiple times.  Once they click next to go on and then use back button on skin to return to the page, things go slightly south.  Interaction continues to work perfect until learner clicks Next button, then the button is totally non-responsive. To reiterate, there are NO advance actions on Next button, just a Jump to Slide.

Have tried practically everything, including copying all slides and pasting into a new blank CPTX file.  Any ideas?

And so you shall have it....

This code executes on entering the quiz slide and is designed to simply hide checkmarks and show buttons and zero out varibles that are meant to be zero for false and 1 for true.

QuizCheckedA-D are check mark graphics that appear when you click a choice.

QuizClear, QuizSubmit, and QuizNext are buttons.  QuizRightCap and QuizLeftCap are captions that appear on scoring.  QuizASelected - QuizDSelected are toggle variables for selected choices; zero when false and 1 when true.

Here is the code executed when you click a clickbox.  It is the same for all four with the exception of the object and variable references.

If the toggle variable for selection is false (0) then we show a checkmark and set the variable to true (1).  If it is not false, then we hide the checkmark and make the variable false (0).

When you click Submit, the following code executes:

Since A, B, and C are correct and D is incorrect, then we check for the three trues and one false.  If so, we show the correct feedback caption and the next button and hide submit and clear.  Clicking Next executes a simple Jump to Slide command.

Otherwise, we show the incorrect feedback and hide submit. They would then click Clear which is simply a next slide command.  On the next slide, which is a blank dummy that lasts for .25 seconds, it has an onExit command to go back to the previous slide (the quiz slide) which executes the onEnter code above and resets everything.

Again, everything works perfect until you advance to the next content slide by clicking Next and then use the back button on the skin (Captivate default) to go back to the quiz slide.  Everything works perfect again until you go to click the Next button and then nothing happens.  Here's the next button's Properties panel:

I tried to keep it simple and really can't figure out why it won't execute the second time around.