No theme in dropdown menu

I get the following error when Creating a chat room:
Fatal error: require_once() [function.require]: Failed opening required '0' (include_path='.:/usr/lib/php:/usr/local/lib/php') in /home/foxwebco/public_html/drupal6/sites/all/modules/phpfreechat/phpfreechat.module on line 548

I left all the settings as their defaults, just entered a "Default Title" and "Default Channels"

I had a look at the settings and I saw that there is no theme in the theme dropdown box under "Chat Room Settings"

Please help me!