ASP.NET Web Application中编写RadioButtonList老是出错的问题

我现在想用ASP.NET Web Application编写个小的程序，试下SP1补丁，写了一个网页，上面就button按钮，一个Label，一个RadioButtonList，实现的功能如下：
protected void Button1_Click(object sender, EventArgs e)
{
Label1.Text = RadioButtonList1.SelectedValue.ToString();
}
但是在debug（F5）的时候，调出的网页在报错，如下
Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately.

Compiler Error Message: CS0426: The type name 'WebForm2' does not exist in the type 'System.Web.UI.WebControls.CheckBox'

Source Error:



Line 112: public webform2_aspx() {
Line 113: string[] dependencies;
Line 114: ((CheckBox.WebForm2)(this)).AppRelativeVirtualPath = "~/WebForm2.aspx";
Line 115: if ((global::ASP.webform2_aspx.@__initialized == false)) {
Line 116: dependencies = new string[1];


Source File: c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\root\5dcce09d\1a79a36\App_Web_webform2.aspx.cdcab7d2._t1a-fyd.0.cs Line: 114

各位高手给指点下这是什么原因？
PS：用ASP.NET Web Site建立就不会出现这样的问题