OnChange Code Not Working With Multiple Forms

[WanamakerMedia]

I am completely new to AJAX, so I got this code from another site and installed it for what I need. It works great if I have only one form on the page ... however, once I have multiple forms on the page, it stops working but it doesnt throw an error code, so I have no clue where to look. Any help would be appreciated!

Select Field Code:

onChange="showField(this.value, 'QQTrim')"

Ajax.js:

function GetXmlHttpObject() {
	var xmlHttp=null;
	try {
		xmlHttp=new XMLHttpRequest();
	}
		catch (e) {
			try {
				xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
			}
		catch (e) {
			xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
		}
	}
	return xmlHttp;
}

function showField(str, id){
	var url="inc/ajaxforms.php"
	url=url+"?modField="+id
	url=url+"&modString1="+str
	url=url+"&sid="+Math.random()
	xmlHttp=GetXmlHttpObject();
	xmlHttp.onreadystatechange= function() {
        if (xmlHttp.readyState==4)
            if (xmlHttp.status==200)
                writeHTML(xmlHttp, id);
    }
    xmlHttp.open("GET",url,true);
    xmlHttp.send(null);	
}

function writeHTML(req, id) {
    document.getElementById(id).innerHTML = req.responseText;
}

[WebGeek182]

Have you checked to make sure they are not using the same id?