哪位高手能帮小弟我看一上！返回值为空，咋回事啊_ASP.NET

谁能帮我看一下！！急！急！急！急！急！返回值为空，怎么回事啊？
我在一个页面里面这么写的：

JScript code

function dealSelectAccount(sender) {        var result = window.showModalDialog("ProjectTypeList.aspx", "", "dialogWidth:540px;dialogHeight:255px;dialogLeft:300px;dialogTop:250px;center:yes;help=no;resizable:no;status:no;scroll=yes");        alert(result);

然后我在新打开的页面里面这么写的：

C# code

protected void btn1_Click(object sender, EventArgs e)        {            for (int i = 0; i < this.treeList.Nodes.Count;i++ )            {                if(treeList.CheckedNodes[i].Checked==true)                {                    Session["ID"] = treeList.CheckedNodes[i].Value.ToString();                    Session["NAME"] = treeList.CheckedNodes[i].Text.ToString();                    string tmp = Session["NAME"].ToString();                    Response.Write(" <Script language='JavaScript'> window.opener=null;window.open('about:blank','_self');window.returnValue = '" + Session["NAME"].ToString() + "';window.close();</Script>");                    break;                }            }         }

问题在于alert(result);为空，怎么回事啊？

------解决方案--------------------------------------------------------
window.opener=null;window.open('about:blank','_self');

写这些无用的代码多此一举
------解决方案--------------------------------------------------------

C# code

页面B：点击B上的（html）img执行function RetrunVal()function RetrunVal(){    var obj = window.dialogArguments;                   obj.value1=document.form1.ddlB.value;                   window.returnValue = obj;                   window.close();}页面A:在页面A加入TextBox1function OpenDialog(Url){  var t1;var obj=showModalDialog(url,window,"dialogHeight:200px;dialogWidth:500px"); if(obj != undefined)          {              t1= obj.value1;              eval("form1.TextBox1.value='"+TextBox1Name+"'");              eval("form1.TextBox1.blur()");          }}