title: Getting Null value on parameter in querystring parameter
body: <p>in my application i have send one link to User's email  id  he can download software on clicking this link....now  my url is look like....
  <a href="http://www.abc.co.in/Download.aspx?period=11/04/2013%2012:29:20%20PM&amp;ProductName=Otja" rel="nofollow">http://www.abc.co.in/Download.aspx?period=11/04/2013%2012:29:20%20PM&amp;ProductName=Otja</a>
  and my code for retriving this value on pageload  download.aspx page is </p>
  
  <pre><code>    string PName = Request.QueryString["ProductName"] as string;
  
  
  
      string myDate = Request.QueryString["period"];
      if (!String.IsNullOrEmpty(myDate))
      {
          myDate = myDate.Replace("!", ":");
      }
      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
      {
  
          lblmsg.Visible = true;
          lblmsg.Text = "U can Still Download";
      }
  </code></pre>
  
  <p>but this is not working  i tested  and before 5 Minute and after  minutes it is only shows  "You can still download"  so i think my error  is  that i can not retrive  that productname and period value on querystring on this download.aspx page..please help me.. thanks 
  i think  there should be error..... String was not recognized as a valid DateTime.  thats why it is pass null value  so any solution ???</p>