Pro Sites gives error in multisite signup page

Hello,
I have Pro Sites installed on my multisite, at Sophire.com, and when going to sophire.com/wp-signup.php , it shows the following error with the Pro Sites plugin:

Warning: array_keys() expects parameter 1 to be array, null given in /home/sophie36/public_html/wp-content/plugins/pro-sites/pro-sites-files/lib/ProSites/View/Front/Checkout.php on line 108

Thank You for your help.