Need help with some logic

In this script i've three dropdown first two set the values for third one. But after 2 or 3 selection it doesn't work.

Im trying something like this http://www.clearpack.com/corp-Search.asp (work on IE)

<?php
$industry = $package = $type = null; //declare vars
$conn = mysql_connect('localhost', ' ', ' ');
$db = mysql_select_db(' ',$conn);
if(isset($_GET["industry"]) && is_numeric($_GET["industry"]))
{
	$industry = $_GET["industry"];	
}
if(isset($_GET["package"]) && is_numeric($_GET["package"]))
{
	$industry = $_GET["package"];
}
if(isset($_GET["type"]) && is_numeric($_GET["type"]))
{
    $type = $_GET["type"];
}
?>

<script language="JavaScript">
function autoSubmit()
{
    var formObject = document.forms['theForm'];
    formObject.submit();
}
</script>

<form name="theForm" method="get">
    <select name="industry" style="width: 150px" onChange="autoSubmit();">        
        <option value="null">Select BY INDUSTRY</option>
        <?php
        //POPULATE DROP DOWN MENU WITH INDUSTRY
        $sql = "SELECT PRODUCT_ID, PRODUCT_NAME FROM TBL_SEARCH WHERE RE_ID = 1";
        $countries = mysql_query($sql,$conn);
        while($row = mysql_fetch_array($countries))
        {        
            echo ("<option value=\"$row[PRODUCT_ID]\" " . ($industry == $row["PRODUCT_ID"] ? " selected" : "") . ">$row[PRODUCT_NAME]</option>");        
        }
        ?>        
    </select> 

       <select name="package" style="width: 150px" onChange="autoSubmit();">        
        <option value="null">Select BY Pakaging</option>  
        <?php        
        //POPULATE DROP DOWN MENU WITH PACKAGING         
        $sql = "SELECT PRODUCT_ID, PRODUCT_NAME FROM TBL_SEARCH WHERE RE_ID = 2";
        $countries = mysql_query($sql,$conn);        
        while($row = mysql_fetch_array($countries))
        {        
            echo ("<option value=\"$row[PRODUCT_ID]\" " . ($industry == $row["PRODUCT_ID"] ? " selected" : "") . ">$row[PRODUCT_NAME]</option>");        
        }        
        ?>        
    </select>    
    
    <br><br>
    
    <?php    
    if($industry != null && is_numeric($industry))
    {    
    ?>    
    <select name="type" onChange="autoSubmit();">
        <option value="null">Select</option>        
        <?php        
        //POPULATE DROP DOWN MENU WITH PRODUCT TYPE FROM A GIVEN INDUSTRY OR PACKAGING       
        $sql = "SELECT TYPE_ID, PRODUCT_TYPE FROM TBL_TYPE WHERE PRODUCT_ID = $industry ";
        $types = mysql_query($sql,$conn);        
        while($row = mysql_fetch_array($types))
        {
            echo ("<option value=\"$row[TYPE_ID]\" " . ($type == $row["TYPE_ID"] ? " selected" : "") . ">$row[PRODUCT_TYPE]</option>");        
        }        
        ?>            
    </select>    
    <?php    
    }    
    ?>    
    <br><br>    
</form>

PHP: