title: System.Data.DuplicateNameException in DataTable
body: <p>I am adding columns dynamically to a static Data table in the !IsPostBack.</p>
  
  <pre><code>static DataTable dtflow = new DataTable();
  
  protected void Page_Load(object sender, EventArgs e)
      {
  
          if (!IsPostBack)
          {
              dtp.Columns.Add("slno");
              dtp.Columns.Add("portname");
              dtp.Columns.Add("type");
              dtp.Columns.Add("portid");
              dtp.Columns.Add("longitude");
              dtp.Columns.Add("latitude");
              dtp.Columns.Add("add1");
              dtp.Columns.Add("add2");
              dtp.Columns.Add("dist");
              dtp.Columns.Add("state");
              dtp.Columns.Add("country");
          }
      }
  </code></pre>
  
  <p>But when I run my website for second time it shows an Exception like this</p>
  
  <blockquote>
    <p><em>Exception Details: System.Data.DuplicateNameException: A column named 'slno' already belongs to this DataTable.</em></p>
  </blockquote>
  
  <p>Can anybody tell me how to resolve this problem</p>