Multiple calls to ajax script not working

Question

I am very new (literally less than a few days) to all things ajax, but it is required for a form I am building for my employer.

Basically, no matter what I do it just will not work for more than one function. To elaborate, I am trying to update 4 different parts of a page based on one drop down using onchange. Now updating one part works fine, updating any more than that fails... but not only fails, it also fails if for example I do call to ajax part, then just a simple alert... but if I do it with the alert first it works, then falls over again if I put anything after the ajax call. I hope that makes sense. It also works if I do, for example onchange, and onblur on the same element, it will execute twice. I'll post the code then hopefully it will make more sense.

<select name="pType" id="ptype" onchange="dostuff()">

So that's the input element...

<script type="text/javascript">
function dostuff(){
ajaxpage('adminincludes/popoptions.php?pID=<?= $sql['pID']; ?>&pType=' + ptype.value,'options');
alert('test');
}
</script>

...and that's the dostuff code, or an example anyway, ignore the PHP part as it fails regardless of that, that part works fine.

Now the rest of the code is within an external file and I believe that somewhere in there is where the problem lies... however I am new to ajax, and am not the greatest with js as I have never really had a major need for it so just learned what I needed, when I needed.

var bustcachevar = 1 //bust potential caching of external pages after initial request? (1=yes, 0=no)
var loadedobjects = ""
var rootdomain = "http://" + window.location.hostname
var bustcacheparameter = ""

function ajaxpage(url, containerid) {
    var page_request = false
    if (window.XMLHttpRequest) // if Mozilla, Safari etc
    page_request = new XMLHttpRequest()
    else if (window.ActiveXObject) { // if IE
        try {
            page_request = new ActiveXObject("Msxml2.XMLHTTP")
        } catch (e) {
            try {
                page_request = new ActiveXObject("Microsoft.XMLHTTP")
            } catch (e) {}
        }
    } else
    return false
    page_request.onreadystatechange = function () {
        loadpage(page_request, containerid)
    }
    if (bustcachevar) //if bust caching of external page
    bustcacheparameter = (url.indexOf("?") != -1) ? "&" + new Date().getTime() : "?" + new Date().getTime()
    page_request.open('GET', url + bustcacheparameter, true)
    page_request.send(null)
    page_request.send(null)
}

function loadpage(page_request, containerid) {
    if (page_request.readyState == 4 && (page_request.status == 200 || window.location.href.indexOf("http") == -1)) document.getElementById(containerid).innerHTML = page_request.responseText
}

function loadobjs() {
    if (!document.getElementById) return
    for (i = 0; i < arguments.length; i++) {
        var file = arguments[i]
        var fileref = ""
        if (loadedobjects.indexOf(file) == -1) { //Check to see if this object has not already been added to page before proceeding
            if (file.indexOf(".js") != -1) { //If object is a js file
                fileref = document.createElement('script')
                fileref.setAttribute("type", "text/javascript");
                fileref.setAttribute("src", file);
            } else if (file.indexOf(".css") != -1) { //If object is a css file
                fileref = document.createElement("link")
                fileref.setAttribute("rel", "stylesheet");
                fileref.setAttribute("type", "text/css");
                fileref.setAttribute("href", file);
            }
        }
        if (fileref != "") {
            document.getElementsByTagName("head").item(0).appendChild(fileref)
            loadedobjects += file + " " //Remember this object as being already added to page
        }
    }
}

Now like I said, the code works perfectly when only calling ajaxpage() once, or multiple times via different events, it just will not work multiple times from one event, even when putting the multiple instances into the dostuff() function.

Any help would be greatly appreciated as this is really starting to aggravate me.

UPDATE: This isn't as urgent now as i have done a "workaround" which uses multiple events such as mouseover, mouseout etc on an update link instead. which means it works as i need it to, however it is not elegant by any means and I am still intrigued why it won't work when called multiple times within 1 event?!