Feedback forms (again)!

I had this problem yesterday which I thought I had solved but I cannot get this to work inside a Feedback form. I have created a sample to explain my problem.

 I have a tick box in a feedback form. Which I want to stop people progressing to the next slide until it is ticked.

I was shown how to do this yesterday which worked but not in a feedback form.

 I hope this helps explain the problem.

 Thank you in advance.

 Rich