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protected void Page_Load(object sender, EventArgs e)
    {
        DataTable dataTable = SqlDataSourceEnumerator.Instance.GetDataSources();

        foreach (DataRow dr in dataTable.Rows)
        {
            if (string.IsNullOrEmpty(dr["InstanceName"].ToString()))
               this.DropDownListInstance.Items.Add(string.Concat(dr["ServerName"]));
            else
               this.DropDownListInstance.Items.Add(string.Concat(dr["ServerName"], "\\", dr["InstanceName"]));
        }
    }