//kode sebelumnya
if(empty($error)){
		
		$cek = mysql_query("SELECT * FROM event WHERE event='$jam' AND date='$tgl'");
		$masuk = mysql_num_rows($cek);
		if($masuk > 0)
		{
			$error['tgl'] = 'Pilih tanggal lain'; 
			$error['jam'] = 'Pilih jam lain'; 
		}
		else
		{
			$in = mysql_query("INSERT INTO event VALUES('','$jam','$name','$phone','$tgl')");
			//echo $jam,$name,$phone,$tgl;
		}
	}                //kode sebelumnya
if(empty($error)){
		
		$cek = mysql_query("SELECT * FROM event WHERE event='$jam' AND date='$tgl'");
		$masuk = mysql_num_rows($cek);
		if($masuk > 0)
		{
			$_SESSION['error'] = $error;  
			$_SESSION['post'] = $_POST; 
			echo '<script type="text/javascript">';
			echo 'alert("Sorry, it is already filled\n Please select the other date");';
			
			echo 'window.location.href="cal.php";';
			echo '</script>';
		}
		else
		{
			$in = mysql_query("INSERT INTO event VALUES('','$jam','$name','$phone','$tgl')");
			//echo $jam,$name,$phone,$tgl;
		}
	}
	else{
		$_SESSION['error'] = $error;  
        $_SESSION['post'] = $_POST;  
        header("location: cal.php"); 
	}Thanks,