Create Directory in ASP.Net

Question

Hi,

I wann to create runtime directory in root folder. By this code

 string strDate = DateTime.Now.ToString("d-M-yyh:mm:ss.ffftt").ToString();

 Directory.CreateDirectory(Server.MapPath("~/Images/Work/") + ddl_category.SelectedItem.Text).CreateSubdirectory(strDate);

But i am getting some error. so please me, How to Create directory with its sub folder at runtime.