DWR同步请求的疑惑

最近在做一个bpm的项目，有个表单需要用DWR远程调用另外一个系统的方法；但在调用过程中出现了问题，这个方法有时候调用得到，有时候又调用不到，觉得是异步请求的关系，所以在代码中将请求设置成了同步，即在调用方法的地方加上了 DWREngine.setAsync(false); 在方法结束的地方加上了DWREngine.setAsync(true);  但仍然出现调用不到得现象。
    代码如下：

DWREngine.setMethod(DWREngine.ScriptTag);
dwr.engine._path = "http://10.0.1.99:7001/Contract/dwr/";
dwr.util._path = "http://10.0.1.99:7001/Contract/dwr/";
SubBankAJAX._path = "http://10.0.1.99:7001/Contract/dwr/";
DWREngine.setAsync(false);
var contextPath = "<%=contextPath%>";
var isSubmit = false;
var max_no = 0;
isForm = true;
//如果为核准按钮时累计金额累加，并要求财务附件上产，如为驳回则财务附件内容清除并付款状态更改

//获得表单
function getForm(){
    return document.all.applyForm;
}

function getAdd(){
    var i = 0;
    var msg = "";
    if (document.getElementById("cw_arriveDate").value.length != 10) {
        i++;
        msg = msg + i + ".收单日期未填写\n";
    }
    
    var cwAttachfiles = document.getElementById("max_no").value;
    if (cwAttachfiles == 0) {
        i++;
        msg = msg + i + ".财务附件未上传";
    }
    else {
        document.getElementById("fileAttach").outerHTML = "<input   name='fileAttach'   type='file' value='' size='50' style='height: 20px'/>";
    }
    if (msg.length > 0) {
        alert(msg);
        return;
    }
    else {
        DWREngine.setAsync(false);
        SubBankAJAX.addPayment(document.getElementById("formEntity.contractNO").value, document.getElementById("formEntity.payMoney").value);
        DWREngine.setAsync(true);
    }
    var form = getForm();
    form.operation.value = "release";
    if (form.onsubmit == null || form.onsubmit.call(form)) {
        var elements = form.getElementsByTagName("input");
        if (elements) {
            for (var i = 0; i < elements.length; i++) {
                if (elements[i].type == "button") 
                    elements[i].disabled = "disabled";
            }
        }
        form.submit();
    }
}

而如果在AJAX请求的地方加上alert，则一定可以调用到；DWREngine.setAsync(false);这个方法会无效呢？ 各位大侠哪位知道，告诉一下谢谢