Comments+ plugin PHP error

We are getting an error when we activate the Comments+ plugin on sweetcode.io. The error is:

method Wdcp_AdminPages::serve() should not be called statically in /home/sweetcode/public_html/wp-content/plugins/comments-plus/comments-plus.php on line 81

Warning: session_start(): Cannot send session cache limiter - headers already sent (output started at /home/sweetcode/public_html/wp-content/plugins/comments-plus/comments-plus.php:81) in /home/sweetcode/public_html/wp-content/plugins/comments-plus/lib/external/facebook/facebook.php on line 49

The site is running PHP 7. Thank you for your help.