Having the player enabled makes editing post load a blank page

Fatal error: Uncaught Error: Call to undefined function mb_convert_case() in /var/www/html/csttv/wp-content/plugins/fv-wordpress-flowplayer/models/flowplayer.php:1982

Stack Trace
1.
flowplayer::get_languages()
/var/www/html/csttv/wp-content/plugins/fv-wordpress-flowplayer/view/wizard.php:377
2.
include(‘/var/www/html/c…’)
/var/www/html/csttv/wp-content/plugins/fv-wordpress-flowplayer/controller/editor.php:113
3.
fv_wp_flowplayer_edit_form_after_editor(”)
/var/www/html/csttv/wp-includes/class-wp-hook.php:292
4.
WP_Hook->apply_filters(NULL, Array)
/var/www/html/csttv/wp-includes/class-wp-hook.php:316
5.
WP_Hook->do_action(Array)
/var/www/html/csttv/wp-includes/plugin.php:484
6.
do_action(‘admin_footer’, ”)
/var/www/html/csttv/wp-admin/admin-footer.php:78
7.
require_once(‘/var/www/html/c…’)
/var/www/html/csttv/wp-admin/post.php:369
8.
{main}
thrown in /var/www/html/csttv/wp-content/plugins/fv-wordpress-flowplayer/models/flowplayer.php on line 1982