Getting a HTTP error 500 when cancelling

Here is what is in the error_log

[26-Jul-2017 00:49:42 UTC] PHP Fatal error: Call to undefined function boolval() in /home/cfhungler011/public_html/gallatinfitness.com/wp-content/plugins/paid-memberships-pro/preheaders/cancel.php on line 42
[26-Jul-2017 00:49:46 UTC] PHP Fatal error: Call to undefined function boolval() in /home/cfhungler011/public_html/gallatinfitness.com/wp-content/plugins/paid-memberships-pro/preheaders/cancel.php on line 42
[26-Jul-2017 00:49:51 UTC] PHP Fatal error: Call to undefined function boolval() in /home/cfhungler011/public_html/gallatinfitness.com/wp-content/plugins/paid-memberships-pro/preheaders/cancel.php on line 42

here is the code for line 40 to the end:

//are we confirming a cancellation?
if(isset($_REQUEST[‘confirm’]))
$pmpro_confirm = boolval($_REQUEST[‘confirm’]);
else
$pmpro_confirm = false;

if($pmpro_confirm) {
if(!empty($old_level_ids)) {
$worked = true;
foreach($old_level_ids as $old_level_id) {
$worked = $worked && pmpro_cancelMembershipLevel($old_level_id, $current_user->ID, ‘cancelled’);
}
}
else {
$old_level_ids = $wpdb->get_col(“SELECT DISTINCT(membership_id) FROM $wpdb->pmpro_memberships_users WHERE user_id = ‘” . $current_user->ID . “‘ AND status = ‘active'”);
$worked = pmpro_changeMembershipLevel(0, $current_user->ID, ‘cancelled’);
}

if($worked === true && empty($pmpro_error))
{
$pmpro_msg = __(“Your membership has been cancelled.”, ‘paid-memberships-pro’ );
$pmpro_msgt = “pmpro_success”;

//send an email to the member
$myemail = new PMProEmail();
$myemail->sendCancelEmail($current_user, $old_level_ids);

//send an email to the admin
$myemail = new PMProEmail();
$myemail->sendCancelAdminEmail($current_user, $old_level_ids);
} else {
global $pmpro_error;
$pmpro_msg = $pmpro_error;
$pmpro_msgt = “pmpro_error”;
}
}

Andrew the php version is 5.4 running wordpress 4.8

Everything was working great until last week – was there an update?