Problem with activating Pro Sites plugin

I have tried activating Pro Sites on a completely fresh installation of WordPress and when I have tried to activate it I receive an error saying:

Plugin could not be activated because it triggered a fatal error.
Fatal error: Call to undefined function switch_to_blog() in /home/content/01/10218501/html/wp-content/plugins/pro-sites/pro-sites.php on line 194

Please can I have some help getting this resolved?

Many thanks,