update to plugin

I updated this plugin today to version 2.1.6 and when I try to open my pages in WordPress I get a page which has 3 input fields i.e title: Select Action, Select Action: select calendar, Select calendar id. There is nothing else on this page. When I look at page source there is php coding with this at the bottom
<b>Fatal error</b>: Call to a member function permission() on a non-object in <b>/xxxx/xxxxxxx/public_html/wp-content/plugins/booking-system/includes/class-widget.php</b> on line <b>83</b>

I have xxx my personal information out.
I have to deactivate the plugin to get my pages to open again. I have now lost all my bookings from my website as I deleted it and tried to reinstall. What is the problem please

https://wordpress.org/plugins/booking-system/