สร้าง listbox 2 ชั้น แล้วใช้งานไม่ได้ ใน ie6 และก็ firefox ครับ

<script language="javascript">
function showHint1(str){ 
	if (str.length > 0){ 
		var url="return1.asp?id="+str;
		xmlHttp=GetXmlHttpObject(stateChange1);
		xmlHttp.open("GET", url , true);
		xmlHttp.send(null);
	} 
} 
</script>
.
.
.....
	     <tr class="StyleNameB">  <td>&nbsp;</td>
			  <td align="right"><strong>หน่วยงานหลัก:</strong></td>
			  <td align="left"> <select name="oid1" onChange="showHint1(this.options[this.selectedIndex].value);">
				  <option value="0">เลือก</option>
		  <%set RS= Server.CreateObject("ADODB.Recordset")
			    sql1 = "SELECT * FROM site_organize1 order by code " 
				RS.Open sql1, MM_data_STRING ,1 ,1
				for i=1 to RS.recordcount 
				     if oid1="" then 
					   if i=1 then  oid1=RS("id") end if
					 end if
				%>
          <option value="<%=RS("id")%>" <%if num(oid1)=num(RS("id")) then response.Write("selected") end if%>><%=rs("name")%>[<%=rs("code")%>]</option>
		  <% rs.movenext
		        next
				rs.close() : set rs=nothing
		     %>
                  </select></td>
			  </tr>
			  	   <tr class="StyleNameB">  <td>&nbsp;</td>
                    <td align="right"><strong>หน่วยงานรอง:</strong></td>
                    <td  align="left"><div id="mypid"><select name="oid2">
                       <option value="0">เลือก</option>
                       <%set RS= Server.CreateObject("ADODB.Recordset")
			    sql1 = "SELECT * FROM site_organize2 where oid1="&num(oid1)&" order by code" 
				RS.Open sql1, MM_data_STRING ,1 ,1
				for i=1 to RS.recordcount 		%>
                       <option value="<%=RS("id")%>" <%if num(oid2)=num(RS("id")) then response.Write("selected") end if%>><%=rs("name")%>[<%=rs("code")%>]</option>
                       <% rs.movenext
		        next
				rs.close() : set rs=nothing
		     %>
                     </select>
			 	
			</div></td></tr>

var xmlHttp

function stateChange1(){ 
	if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete"){ 
	document.getElementById("mypid").innerHTML=xmlHttp.responseText 
	} 
} 

function GetXmlHttpObject(handler)
{ 
var objXmlHttp=null

if (navigator.userAgent.indexOf("Opera")>=0)
{
alert("This example doesn't work in Opera") 
return 
}
if (navigator.userAgent.indexOf("MSIE")>=0)
{ 
var strName="Msxml2.XMLHTTP"
if (navigator.appVersion.indexOf("MSIE 5.5")>=0)
{
strName="Microsoft.XMLHTTP"
} 
try
{ 
objXmlHttp=new ActiveXObject(strName)
objXmlHttp.onreadystatechange=handler 
return objXmlHttp
} 
catch(e)
{ 
alert("Error. Scripting for ActiveX might be disabled") 
return 
} 
} 
if (navigator.userAgent.indexOf("Mozilla")>=0)
{
objXmlHttp=new XMLHttpRequest()
objXmlHttp.onload=handler
objXmlHttp.onerror=handler 
return objXmlHttp
}
}