inline chat not showing with IE9

Hey.
I'm using WP 3.9.1 and chat 1.0.8.1. The inline chat is showing with Firefox, but not with IE9. There is a message in IE (I tried to translate from german):

Message: Function expected
Row: 37
character: 3
Code: 0
URI: http://www.medrelax.ch/MEV-t/?p=223

Message: The object doesn't support thise feature or methode.
Row 106
character: 3
Code: 0
URI: http://www.medrelax.ch/MEV-t/wp-content/plugins/wordpress-chat/js/wpmudev-chat.js?ver=2.0.8.5