跨浏览器Ajax问题

I have created an ajax function that works on chrome and firefox but not i.e 8 can anyone spot the issue?

html section:

<select id='choices'>
<option id="no" value="no" onClick="check()">No</option>
<option value="yes" onClick="check()">Yes</option>
</select>

Javascript section:

function check(){
    var a = document.getElementById("choices").value;
    var type = "label";
    ajaxFunction(a,type);
    if(a == "yes"){
        document.getElementById("results").style.display="block";
    }
    else{
        document.getElementById("results").style.display="none";
    }
}

AJAX Section:

function ajaxFunction(result,dif){
    var ajaxRequest;  // The variable that makes Ajax possible!

    try{
        // Opera 8.0+, Firefox, Safari
        ajaxRequest = new XMLHttpRequest();
    } catch (e){
        // Internet Explorer Browsers
        try{
            ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
        } catch (e) {
            try{
                ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
            } catch (e){
                // Something went wrong
                alert("Your browser broke!");
                return false;
            }
        }
    }
    // Create a function that will receive data sent from the server
    ajaxRequest.onreadystatechange = function(){
        if(ajaxRequest.readyState == 4){
            if(dif == "label"){
                var ajaxDisplay = document.getElementById('results');
            }
            else{
                var ajaxDisplay = document.getElementById('results1');
            }
            ajaxDisplay.innerHTML = ajaxRequest.responseText;
        }
    }
    if(dif == "label"){
        var hiddenvalue = document.getElementById('hiddenvalue').value;
        var queryString = "?type=" + result + "&label=" + hiddenvalue + "&dif=" + dif;
    }
    else{
        var queryString = "?type=" + result + "&dif=" + dif;
    }

    ajaxRequest.open("GET", "scripts/script.php" + queryString, true);
    ajaxRequest.send(null); 
}

PHP Section:

var_dump($_GET);

I'm not sure if this is just a compatability issue or not as i have used very similar code to this in another project which worked fine however i also have a couple of other scripts that are loading in such as jquery 1.2.3 and google analytics (with there advanced link tracker which i had to get rid of as it was throwing an error). I have checked the debugger and clicked break all on error and i can click about on the onclick but no error actually shows in the debugger. Has anyone got any sugestions other then jquery (can't get my head around it)

IE does not suppot onclick on an option.

onchange needs to be on the select.

<select id='choices' onchange="check()">
    <option id="no" value="no">No</option>
    <option value="yes">Yes</option>
</select>