PHP error: Undefined array key “data_tabs”

PHP Warning:  Undefined array key "data_tabs" in /chroot/home/USER_NAME/html/wp-content/plugins/facebook-pagelike-widget/fb_class.php on line 36

This looks to be related to the poor handling of this check, I’d suggest checking that the property exists first. That should help fix this error.

if($instance['data_tabs'] != '')
// to
if (array_key_exists('data_tabs', $instance) && $instance['data_tabs'] !== '')