Problem with async javascript pro and not able to leave ticket on website.

[02-May-2017 23:45:02 UTC] PHP Fatal error: Uncaught Error: Call to undefined function is_plugin_active() in /home/madmax/public_html/neufsvies/wp-content/plugins/async-javascript-pro/async-javascript-pro.php:88
Stack trace:
#0 /home/madmax/public_html/neufsvies/wp-content/plugins/async-javascript-pro/async-javascript-pro.php(28): AsyncJavaScriptPro->aj_admin_init()
#1 /home/madmax/public_html/neufsvies/wp-content/plugins/async-javascript-pro/async-javascript-pro.php(1581): AsyncJavaScriptPro->__construct()
#2 /home/madmax/public_html/wp-settings.php(304): include_once(‘/home/madmax/pu…’)
#3 /home/madmax/public_html/wp-config.php(129): require_once(‘/home/madmax/pu…’)
#4 /home/madmax/public_html/wp-load.php(37): require_once(‘/home/madmax/pu…’)
#5 /home/madmax/public_html/wp-blog-header.php(13): require_once(‘/home/madmax/pu…’)
#6 /home/madmax/public_html/index.php(17): require(‘/home/madmax/pu…’)
#7 {main}
thrown in /home/madmax/public_html/neufsvies/wp-content/plugins/async-javascript-pro/async-javascript-pro.php on line 88