Fatal Error (Line 207) on Activation

Hi there!
This plugin seems like the perfect solution for us, however I’m running into a fatal error when attempting to “Activate” it.

Fatal error: Call to undefined method modal_dialog_plugin::modal_dialog_default_config() in /app/wp-content/plugins/modal-dialog/modal-dialog.php on line 207

I’m currently running a WordPress 4.0 on a Multisite Installation.
Any tips?

https://www.ads-software.com/plugins/modal-dialog/