Server Error in '/' Application.

Object reference not set to an instance of an object.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

Line 3351:            sql = "select fatherId, name from info_class where id =" + c;
Line 3352:            OleDbDataReader dr = con.DrSelect(sql, null);
Line 3353:            if (dr.Read())
Line 3354:            {
Line 3355:                cn += loadcolumn(dr["fatherId"].ToString(), con);

Source File: f:\netweb\hl_netweb\App_Code\jss_fc\JSSMethods.cs    Line: 3353

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an object.]
   jss_fc.JSSMethods.loadcolumn(String c, OperateDB con) in f:\netweb\hl_netweb\App_Code\jss_fc\JSSMethods.cs:3353
   jss_fc.JSSMethods.loadcolumn(String c, OperateDB con) in f:\netweb\hl_netweb\App_Code\jss_fc\JSSMethods.cs:3355
   jss_fc.JSSMethods.mt_columnjl(String tagename, OperateDB con, String[] param, String[] idsparam) in f:\netweb\hl_netweb\App_Code\jss_fc\JSSMethods.cs:822
   jss_fc.JSSMethods.TAGES_SINGLE(String tagename, OperateDB con, String[] param, String[] idsparam) in f:\netweb\hl_netweb\App_Code\jss_fc\JSSMethods.cs:207
   info.Page_Load(Object sender, EventArgs e) in f:\netweb\hl_netweb\info.aspx.cs:60
   System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) +14
   System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +35
   System.Web.UI.Control.OnLoad(EventArgs e) +99
   System.Web.UI.Control.LoadRecursive() +50
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +627


Version Information: Microsoft .NET Framework Version:2.0.50727.3053; ASP.NET Version:2.0.50727.3053