Verify that you have typed the URL correctly. If the URL should be serving existing content, the system administrator may need to add a new request URL mapping to the intended application.

string url = "http://ABRLMOREMOSS/";

           using (SPSite siteCollection = new SPSite(url))
           {
               using (SPWeb spWeb = siteCollection.OpenWeb())
               {
                   SPList spList = spWeb.GetList(url);

                   string fileName = "XXXX";
                   FileStream fileStream = null;
                   Byte[] fileContent = null;

                   try
                   {
                       string docPath =Server.MapPath("~/Excel/") + "Report2_Suppliers_OU_Invoice_DATE_HM_15_Dec_2012_1.xlsx"; //physical location of the file
                       fileStream = File.OpenRead(docPath);
                       fileContent = new byte[Convert.ToInt32(fileStream.Length)];
                       fileStream.Read(fileContent, 0, Convert.ToInt32(fileStream.Length));
                       spList.RootFolder.Files.Add(spList.RootFolder.Url + "/" + fileName, fileContent, true);
                       spList.Update();
                   }
                   catch (Exception ex)
                   {

                   }
                   finally
                   {
                       if (fileStream != null)
                       {
                           fileStream.Close();
                       }
                   }
               }
           }