PHP Error: Page pulls up blank! Help!

I’ve been running wordpress for about 4 months without many issues, but I just got a new one that has me totally stumped.

PHP Fatal error: Call to undefined function: mb_internal_encoding() in /usr/home/gogelajc/domains/gogela.com/public_html/blog/wp-content/plugins/bdprss/bdp-rssfeed.php on line 5

Does anyone know how I can resolve this problem? The blog is located at https://www.gogela.com/blog The site resolves the URL, the database is running fine, and my redirect page from gogela.com/index.html is fine and dandy too….

is there anything I can do to disable the plugins? Would that even help? Any advice anyone could offer would be most appreciated.