Variable not doing its job

Hello everyone,

I have a question regarding a problem that I encountered. I have on one slide some boxes where the user has to click on them and find the correct answer. He is allowed to go further to the next slide only when he clicked on the correct box with the correct answer. Now, my problem is that after I click on that box with the correct answer, I move on to the next slide, than I want to go back to the previous slide, when I click the "next" button it's not going further. I have attached here this part of the project in order to understand the issue better.

Thanks in advance for your help.

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