SmartCrawl throws a 500 error when saving a post as draft

After updating SmartCrawl I started getting a 500 server error when I try to save posts or pages as draft. I checked the debug log and found this
Fatal error: Uncaught Error: Call to undefined function mb_detect_encoding() in /wp_content/content/plugins/wpmu-dev-seo/includes/external/simple_html_dom.php:1234