Tried Installing pro sites but having error.

I have uploaded the pro sites and i click activated it shows me this.

"Plugin could not be activated because it triggered a fatal error.

Fatal error: Call to undefined function switch_to_blog() in /nfs/c10/h05/mnt/141878/domains/market.sghumor.com/html/wp-content/plugins/pro-sites/pro-sites.php on line 190"

I have no idea why.