Hi,
in fact there was a similar issue with the SEO plugin by Sick^. Here is the corresponding German thread here in the Bastelstu.be: Ungültiger Link. As you don't understand German and Google translate is pretty bad for technical language I'll ask you some questions in English below
Which is the folder you installed the chat into? What does show up in the address bar when you click the main menu item? Can you disable the debug mode, try to enter the chat, open the page source (using Ctrl+U), search for wcf\system\exception\IllegalLinkException thrown in and provide me the following stack trace?