Workaround for the WP Login Security 2 plugin issuing "session_start(): Cannot send session cache limiter" warnings where the PHP display_errors ini setting can't be changed.

wp-login-security-2-fix.php

<?php

function wpls2_new_ip_check() {
        $error_status = ini_get('display_errors');
        if ($error_status === '1') {
		ini_set('display_errors', '0');
	}
	global $wpls2_options, $current_user;
	session_start();
	$known = get_option( $wpls2_options['whitelist'] );
	$user = $current_user->user_login;
	$ip = $_SERVER['REMOTE_ADDR'];
	
	// First check for known and activated IP
	if ( is_array($known) && $known[ $user ][ $ip ]['activated'] == true ) {
		if ($error_status === '1') {
			ini_set('display_errors', $error_status);
		}
		return false; // This is a known IP
	}
	 
	// Then check for IPKEY indicating  registration
	elseif (isset($_SESSION['wpls2_ipkey']) ) {

		$ipkey = $_SESSION['wpls2_ipkey'];
		if ( $known[ $user ][ $ip ][ 'ipkey' ] == $ipkey ) {  
			// Key valid.  Login.
			// TODO Add check to verify key expired keys
			$known[ $user ][ $ip ]['date_activated'] = date(WPLS2_DATE_FORMAT);
			$known[ $user ][ $ip ]['activated'] = true;
			unset( $_SESSION['wpls2_ipkey'] );
			
			update_option( $wpls2_options['whitelist'] , $known );

			if ( $_options['notify_both'] ) {
				wpls2_notify_blog_admin();
			}
			if ($error_status === '1') {
				ini_set('display_errors', $error_status);
			}
			return false;

		} else {  
		    wp_logout();
			//wp_redirect( site_url('wp-login.php?action=invalidkey') );
			
			// Redirect using javascript to avoid problem with output buffering.
			echo "<script> document.location.href='".site_url('wp-login.php?action=invalidkey')."'</script>";
			exit;
		}
	}
	// If not known or registering, notify of new IP
	else {
		wpls2_send_activation();
		wp_logout();
		//wp_redirect(site_url('wp-login.php?action=unknownip'));
		
		// Redirect using javascript to avoid problem with output buffering.
		echo "<script>document.location.href='".site_url('wp-login.php?action=unknownip')."'</script>";
		exit;
	}
	 
}

?>