C# 为什么我不能使用“Invokemember”（“click”）`以编程方式单击我的按钮？

我正试图通过

WebBrowserControl

从应用程序中的网站获取数据。我可以成功登录，但当我以编程方式调用

btnsearch.Invokemember（“单击”）

时，我收到一个JavaScript错误。如果我以交互方式单击

WebBrowserControl

上的按钮，则不会收到任何错误，一切正常

在aspx页面中，我有一个JavaScript函数用于调用Ajax面板：

<script type="text/javascript">
/*<![CDATA[*/   
window["ctl00_WorkSpace_ctlCustAVIHistory_ajxResultPanel"] = new RadAjaxPanelNamespace.RadAjaxPanel({ClientID:"ctl00_WorkSpace_ctlCustAVIHistory_ajxResultPanel",EnableOutsideScripts:false,EnablePageHeadUpdate:true,Url:"/app/ModuleCustomer/ViewAVITransactions.aspx",LoadingPanelID:"ctl00_WorkSpace_ctlCustAVIHistory_LoadingPanel1",ActiveElementID:"",ClientEvents:{OnRequestStart:"",OnRequestSent:"",OnResponseReceived:"",OnResponseEnd:""},FormID:"aspnetForm",UniqueID:"ctl00$WorkSpace$ctlCustAVIHistory$ajxResultPanel"});/*]]>*/
</script>

知道为什么会这样吗

    private const string STR_Field_userid = "field_userid";
    private const string STR_Field_password = "field_password";
    private const string STR_Submit = "submit";            

        document.GetElementById(STR_Field_userid).InnerText = UserId;
        document.GetElementById(STR_Field_password).InnerText = Password;
        document.Forms[0].InvokeMember(STR_Submit);

    private const string STR_Field_userid = "field_userid";
    private const string STR_Field_password = "field_password";
    private const string STR_Submit = "submit";            

        document.GetElementById(STR_Field_userid).InnerText = UserId;
        document.GetElementById(STR_Field_password).InnerText = Password;
        document.Forms[0].InvokeMember(STR_Submit);