以下是代码,红色的错误,鼠标放上去显示:"class System.IO.Directory 公开应用于创建 移动和枚举通过目录和子目录和静态方法,无法继承此类."

浏览器显示错误是:"编译器错误信息: CS0723: 无法声明静态类型“System.IO.Directory”的变量"

protected void Page_Load(object sender, EventArgs e)
{
string strDir2List = Request.QueryString.Get("dir");
Directory thisOne = null;
try
{
thisOne = new Directory(Dir2List);
//Reading the directory properties
Response.Write("<p>Creation:" + thisOne.CreationTime.ToString() + "</p>");
Directory[] subDirectories = thisOne.GetDirectories();
Response.Write("<ul>");
for (int i = 0; i < subDirectories.Length; i++)
{
Response.Write("<li><a href=\'listdir.aspx?dir=Server.UrlEncode(subDirectories[i].FullName)''\'>" + subDirectories[i].Name + "</a>");
}
Response.Write("<ul>");
File[] theFiles = thisOne.GetFiles();
Response.Write("ul");
for (int i = 0; i < theFiles.Length; i++)
{
Response.Write("<li><a href=\'showfile.aspx?file=Server.UrlEncode(theFile[i].FullName)''\'>" + theFiles[i].Name + "</a>");
}
Response.Write("/ul");
}
catch (Exception e)
{
Response.Write("Access not possible.error:<i>" + e.ToString + "</i>");
Response.End();
}
}

编译错误
说明: 在编译向该请求提供服务所需资源的过程中出现错误。请检查下列特定错误详细信息并适当地修改源代码。

编译器错误信息: CS0721: “System.IO.Directory”: 静态类型不能用作参数

源错误:

行 18:
行 19: }
行 20: protected void RecursiveDump(Directory theDir, int nLevel)
行 21: {
行 22: Directory[] subDirectories = theDir.GetDirectories();



也是Directory 这个错误,教程上是这样写的,怎么回事呀??