Error when trying to Customize my site

I tried all versions of WP activate/deactivate plugins but the issue still apears. I’ve installed demo data I followed all the installation procedure but still Can’t take Customize my site from browser. When I click appearence -> Customize every time I take critical error. I’ve purchased the Political Campaign Pro theme an it uses Ibtana WordPress Website Builder. Please help because I have wasted so much time for nothing!!!!!!