PHP Catchable fatal error: Object of class WP_Error could not be converted to string in ***/wp-content/plugins/gp-premium/elements/class-hero.php on line 848
PHP Catchable fatal error: Object of class WP_Error could not be converted to string in ***/wp-content/plugins/gp-premium/elements/class-hero.php on line 881
So that looks like you had a template tag added to a Page Hero which was causing an error. I would need to know the template tag to know why the error was happening.
Ah okay. Then it was because it had a Smart Slider 3 label. In principle it worked fine but I moved the web to another domain and it broke down there. I re-generated the page and a new page hero with the same shortcode of smar slider 3. Then it worked fine again.