Ho risolto così.
codice:protected void SubmitButton_Click(Object sender, EventArgs e) { HttpFileCollection uploadedFiles = Request.Files; String id = Request.QueryString["id"]; for (int i = 0; i < uploadedFiles.Count; i ++) { UploadAndResizeAnImage(uploadedFiles[i], 1800.0, 1200.0, "/images/foto/" + id, true); Response.Redirect("chiudi.asp"); } }