PHP Error with WMPU DEV plugin

Am looking for insight into 2 PHP errors:

1— [18-Jan-2016 13:45:59 UTC] PHP Fatal error: Call to undefined function is_plugin_active() in /home/spiritu2/public_html/wp-content/plugins/wpmudev-updates/includes/class-wpmudev-dashboard-api.php on line 541

2— [20-Jan-2016 00:33:00 UTC] PHP Warning: strip_tags() expects parameter 1 to be string, array given in /home/spiritu2/public_html/wp-admin/update-core.php on line 300

Thanks in advance for your time

David