Fatal Error

Hi I have added the code to my wp-config.php file but when I go to activate the plugin I keep getting the error message:

Plugin could not be activated because it triggered a fatal error.
This plugin needs the activation of the multisite-feature for working properly. Please read this post if you don’t know the meaning.

I have followed exactly the instructions in the mentioned post but it’s still coming up with this error.

Any ideas how to fix this?

Thanks!

http://ww.wp.xz.cn/extend/plugins/multisite-language-switcher/