Getting error when activating plugin after update

After updating to the new version (1.1) today, I’m getting the following error messages on my website:

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Strict Standards: Declaration of Walker_PostExpirator_Category_Checklist::start_lvl() should be compatible with Walker::start_lvl(&$output, $depth = 0, $args = Array) in E:\Websites\domain.com\wp-content\plugins\post-expirator\post-expirator.php on line 1291 Strict Standards: Declaration of Walker_PostExpirator_Category_Checklist::end_lvl() should be compatible with Walker::end_lvl(&$output, $depth = 0, $args = Array) in E:\Websites\domain.com\wp-content\plugins\post-expirator\post-expirator.php on line 1291 Strict Standards: Declaration of Walker_PostExpirator_Category_Checklist::start_el() should be compatible with Walker::start_el(&$output, $object, $depth = 0, $args = Array, $current_object_id = 0) in E:\Websites\domain.com\wp-content\plugins\post-expirator\post-expirator.php on line 1291 Strict Standards: Declaration of Walker_PostExpirator_Category_Checklist::end_el() should be compatible with Walker::end_el(&$output, $object, $depth = 0, $args = Array) in E:\Websites\domain.com\wp-content\plugins\post-expirator\post-expirator.php on line 1291 Notice: Undefined index: WP_Widget_Recent_Comments in E:\Websites\domain.com\wp-content\themes\directory\lib\cleanup.php on line 13 Notice: Undefined index: eventDisplay in E:\Websites\domain.com\wp-content\themes\directory\lib\custom-events.php on line 157
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Any ideas what could be triggering this?
Thanks!

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