I have the following ajax call and it always hits the error callback function every time it is called. The code in the handler is still run after the error but the success callback is never executed. What have I got wrong?

 $.ajax({
        type: "POST",
        url: "Handlers/TheHandler.ashx",
        data: {
            control1: $('[id*=control1]').val(),
            control2: $('[id*=control2]').val(),
            control3: $('[id*=control3]').val(),
            control4: $('#control4').val(),
            control5: $('[id*=control5]').val(),
            control6: $('[id*=control6]').val()
        },
        error: function (jqXHR, textStatus, errorThrown) {
            alert(jqXHR.readyState);
            alert(textStatus);
            alert(errorThrown);
        },
        success: function (returnedValue) {
            alert("Got Here");
            alert(returnedValue);
        }
    });