Fatal error: Uncaught Error: Call to undefined function mb_strtoupper()
in /home/aboeliwd/public_html/wp-content/plugins/wordpress-seo/src/generators/schema/article.php on line 226

Call stack:

1. Yoast\W\S\G\S\Article::word_count()
   wp-content/plugins/wordpress-seo/src/generators/schema/article.php:60
2. Yoast\W\S\G\S\Article::generate()
   wp-content/plugins/wordpress-seo/src/generators/schema-generator.php:128
3. Yoast\W\S\G\Schema_Generator::generate_graph()
   wp-content/plugins/wordpress-seo/src/generators/schema-generator.php:75
4. Yoast\W\S\G\Schema_Generator::generate()
   wp-content/plugins/wordpress-seo/src/presentations/indexable-presentation.php:720
5. Yoast\W\S\P\Indexable_Presentation::generate_schema()
   wp-content/plugins/wordpress-seo/src/presentations/abstract-presentation.php:66
6. Yoast\W\S\P\Abstract_Presentation::__get()
   wp-content/plugins/wordpress-seo/src/presenters/schema-presenter.php:61
7. Yoast\W\S\P\Schema_Presenter::get()
   wp-content/plugins/wordpress-seo/src/presenters/schema-presenter.php:45
8. Yoast\W\S\P\Schema_Presenter::present()
   wp-content/plugins/wordpress-seo/src/integrations/front-end-integration.php:406
9. Yoast\W\S\I\Front_End_Integration::present_head()
   wp-includes/class-wp-hook.php:324
10. WP_Hook::apply_filters()
    wp-includes/class-wp-hook.php:348
11. WP_Hook::do_action()
    wp-includes/plugin.php:517
12. do_action()
    wp-content/plugins/wordpress-seo/src/integrations/front-end-integration.php:377
13. Yoast\W\S\I\Front_End_Integration::call_wpseo_head()
    wp-includes/class-wp-hook.php:324
14. WP_Hook::apply_filters()
    wp-includes/class-wp-hook.php:348
15. WP_Hook::do_action()
    wp-includes/plugin.php:517
16. do_action()
    wp-includes/general-template.php:3065
17. wp_head()
    wp-content/themes/mht/header.php:50
18. require_once()
    wp-includes/template.php:810
19. load_template()
    wp-includes/template.php:745
20. locate_template()
    wp-includes/general-template.php:48
21. get_header()
    wp-content/themes/mht/single.php:10
22. include()
    wp-includes/template-loader.php:106
23. require_once()
    wp-blog-header.php:19
24. require()
    index.php:17