ช่วยดู ajax listbox ให้ผมทีครับ มันไม่ส่งค่าให้ งง อะครับ

<script language = "JavaScript">
		//**** List Class (Start) ***//
		function ListClass(SelectValue)
		{
			frmMain.ddlClass.length = 0
			
			//*** Insert null Default Value ***//
			var myOption = new Option('','')  
			frmMain.ddlClass.options[frmMain.ddlClass.length]= myOption
			
			<?
			$strSQL = "SELECT * FROM TB_CLASS";
			$objQuery = mysql_query($strSQL) or die ("Error Query [".$strSQL."]");

			$objResult = mysql_fetch_array($objQuery);
			
			for($i=1;$i<=$objResult["tb_class_num"];$i++){
			?>
				x = <?=$i;?>;
				mySubList = new Array();
				
				strGroup = <?=$objResult["tb_building_id"];?>;
				strValue = "<?=$i;?>";
				strItem = "<?=$i;?>";
				mySubList[x,0] = strItem;
				mySubList[x,1] = strGroup;
				mySubList[x,2] = strValue;
				if (mySubList[x,1] == SelectValue){
					var myOption = new Option(mySubList[x,0], mySubList[x,2])  
					frmMain.ddlClass.options[frmMain.ddlClass.length]= myOption					
				}		
				<?php } ?>															
		}
		//**** List Class (End) ***//
</script>


<form name="frmMain" action="" method="post">
	อาคาร
	<select id="ddlBuild" name="ddlBuild" onChange = "ListClass(this.value)">
	<option selected value=""></option>
	<?	
	$strSQL = "SELECT * FROM TB_BUILDING ORDER BY tb_building_id ASC ";
	$objQuery = mysql_query($strSQL) or die ("Error Query [".$strSQL."]");
	while($objResult = mysql_fetch_array($objQuery))
	{
	?>
	<option value="<?=$objResult["tb_building_id"];?>"><?=$objResult["tb_building_name"];?></option>
	<?
	}
	?>
	</select><br>

ชั้น
	<select id="ddlClass" name="ddlClass" style="width:120px" onChange = ""></select><br>
</form>