ช่วยดูโค๊ตให้หน่อยนะครับ ไม่รู้ว่าทำไมถึงไม่ได้ค่าตัวแปล

<?
session_start();
include ('connect.php');
$rdo_lang=$_REQUEST[rdo_lang];
if($chk_lang=='ok'){
	if($rdo_lang!=''){
		$_SESSION['lang']=$rdo_lang;
		echo "<script language='javascript1.4'>
				 window.location='main.php';
				</script>";
	echo $rdo_lang;
}else{
		echo "<script language='javascript1.4'>
				 alert('Please select a language.');
				</script>";
	}
}
?>

<ul id="menu">
	   <li><a href="index.php?chk_lang=ok" >Proprety</a></li>
	   <li><a href="index.php?chk_lang=ok">Traveline Service</a></li>
	   <li><a href="index.php?chk_lang=ok">Import Export</a></li>
	   <li><a href="index.php?chk_lang=ok">Car & Bike Service</a></li>
	   <li><a href="index.php?chk_lang=ok">Contact Us</a></li>
	</ul>	


    <td align="center" valign="middle"><form id="form_lang" name="form_lang" method="post" action="">
      <table width="100%" border="0">
        <tr>
          <td width="79%" align="right" valign="middle"><span id="result_box" lang="en" xml:lang="en"><span title="">Choose language</span></span></td>
          <td width="3%" align="right" valign="middle"><input name="rdo_lang" type="radio" value="th" /></td>
          <td width="4%" align="right" valign="middle"><img src="images/thailand.png" width="32" height="32" /></td>
          <td width="3%" align="right" valign="middle"><input name="rdo_lang" type="radio" value="eng" /></td>
          <td width="4%" align="right" valign="middle"><img src="images/reino_unido.png" width="32" height="32" /></td>
          <td width="3%" align="right" valign="middle"><label>
            <input name="rdo_lang" type="radio" value="arb" />
          </label></td>
          <td width="4%" align="right" valign="middle"><img src="images/egypt.png" width="32" height="32" /></td>