title: String was not recognized as a valid DateTime
body: <p>My code is .......</p>
  
  <pre><code>  string PName = Request.QueryString["ProductName"] as string;
    string myDate = Request.QueryString["period"];
  
   string sql = "select FileName from tblProduct Where ProductName=" + PName;
  
  
  
      DateTime dt1 = Convert.ToDateTime(myDate);
      DateTime dt2 = DateTime.Now;
      TimeSpan variable = dt2 - dt1;
      if (variable.TotalMinutes &gt; 5)
      {
          //Response.Write("Download time is expired now");
          lblmsg.Visible = true;
          lblmsg.Text = "Download time is expired now";
      }
      else
      {
          //string url1 = " http://www.shreehans.co.in/files/" + PName +"";
          //Response .Redirect ()
          lblmsg.Visible = true;
          lblmsg.Text = "U can Still Download";
      }
  </code></pre>
  
  <p>And My URl is  with querystring parameters ......</p>
  
  <p>mail.Body += string.Format("http://www.abc.co.in/Download.aspx?period=" + DateTime.Now + "&amp;ProductName=" + productName + "\">Demo Download"); </p>