var http = false;

    // Creates xmlhttp object
    if (navigator.appName == "Microsoft Internet Explorer") {
        http = new ActiveXObject("Microsoft.XMLHTTP");
    } else {
        http = new XMLHttpRequest();
    }
    http.onreadystatechange = function() {
        if (http.readyState == 4) {
            alert(http.responseText);
        }
    }

    // Functions to calculate optimum layout etc.
    function compute() {
        var statusSpan = document.getElementById("cwStatus");
        document.getElementById("fader").style.display = "";
        document.getElementById("computingWait").style.display = "";

        statusSpan.innerHTML = "<b>Status:</b> Realigning sattelites"
        http.open("GET", "alg.aspx?cr=8&cc=7&sq=3,3", true);

        http.send(null);
    }

This code sort of works, but the querystring data isn't being passed through. It keeps returning an ASPX error page which only happens when there is no querystring data.

Thanks for any help