Fatal error: Uncaught Error: Call to undefined function mb_strimwidth() in /home/qschool/wp-content/plugins/kboard/class/KBContentListTable.class.php:167 Stack trace: #0 /home/qschool/wp-content/plugins/kboard/class/KBContentListTable.class.php(137): KBContentListTable->single_row(Object(stdClass)) #1 /home/qschool/wp-admin/includes/class-wp-list-table.php(1359): KBContentListTable->display_rows() #2 /home/qschool/wp-admin/includes/class-wp-list-table.php(1286): WP_List_Table->display_rows_or_placeholder() #3 /home/qschool/wp-content/plugins/kboard/pages/kboard_content_list.php(32): WP_List_Table->display() #4 /home/qschool/wp-content/plugins/kboard/index.php(732): include_once('/home/qschool/w...') #5 /home/qschool/wp-includes/class-wp-hook.php(292): kboard_content_list('') #6 /home/qschool/wp-includes/class-wp-hook.php(316): WP_Hook->apply_filters('', Array) #7 /home/qschool/wp-includes/plugin.php(484): WP_Hook->do_action(Array) #8 /home/qschool/wp-admin/admin.php(259): do_action('kboard_page_kbo...') #9 {main} thrown in /home/qschool/wp-content/plugins/kboard/class/KBContentListTable.class.php on line 167

이런 오류가 발생합니다. 원인이 무엇인가요?