Plugin installation killed my site. How to recover?

Installed a calendar plugin and now I get this error when trying to get to site:

“Warning: Call-time pass-by-reference has been deprecated; If you would like to pass it by reference, modify the declaration of array_splice(). If you would like to enable call-time pass-by-reference, you can set allow_call_time_pass_reference to true in your INI file in xxxxxxx\html\wp-content\plugins\event-calendar-scheduler\scheduler.php on line 151

Fatal error: Call to undefined function wp_register_sidebar_widget() in D:\xxxxxx\html\wp-content\plugins\event-calendar-scheduler\scheduler.php on line 69″

How can I recover from this?