saat kembali muncul Konfirmasikan Pengiriman Ulang Formulir....ERR_CACHE_MISS

bagaimana cara mengatasinya? method yang kugunakan post.. code penyimpanan 1= bayartahun.php

<form  role="form" method="post" action="?hal=tahunbayar">
  <div class="form-group row">
	<label for="hori-pass1" class="col-sm-4 form-control-label">Nomer Induk Santri</label>
    	<div class="col-sm-3">
      		<input type="text" class="form-control" id="nis" name="kode">
    	</div>
  </div>
</form>

penyimpanan ke 2 : tahunbayar.php

 <?php
    if(isset($_REQUEST['submit'])){
        $nis = $_REQUEST['kode'];

        $query="SELECT a.nis,a.nm_santri
        FROM santri  WHERE nis='$nis' ";

        $result=$mysqli->query($query);
        $num_result=$result->num_rows;
        list($nis,$nm_santri,) = mysqli_fetch_array($result);
?>
<?php
     if ($num_result > 0 ) {
        }
    }
?>

                        <div class="form-group row">
                            <label for="inputEmail3" class="col-sm-3 form-control-label">NIS</label>
                        <div class="col-sm-4">
                            <input type="text" class="form-control" name="kode"   value="<?php echo $nis; ?>" readonly>
                        </div>
                        </div>

                        <div class="form-group row">
                            <label for="hori-pass1" class="col-sm-3 form-control-label">Nama Santri</label>
                        <div class="col-sm-4">
                            <input type="text" class="form-control" name="nama"  value="<?php echo $nm_santri; ?>" readonly>
                        </div>
                        </div>