Hi siteconcursos,
This could be caused by many things, but I don’t think this is an HD Quiz issue, but an issue with however you are generating your sitemap.
HD Quiz uses custom post types to create and store questions, but these questions are not created as pages (set using native WordPress functions) – meaning the pages do not exist.
My guess is that whatever sitemap plugin or generator is not honoring the WordPress 'publicly_queryable' => false
hook and is wrongly including HD Quiz questions in the sitemap. Google reads this incorrect sitemap and gives a 404 warning because the page cannot be found.
I’d suggest going into your sitemap generation plugin and seeing if there is an option to exclude posts by post type.
If you would like further assistance, then please let me know how you are generating and submitting your sitemap.xml to webmaster tools and I can advise from there.