Migrate IIS 6 to 7.5, NullReferenceException: Object reference not set to an instance of an object.

We are in the process of migrate from old system: windows 2003 / IIS 6 ==> new system:windows 2008 r2 / IIS 7.5

We used msdeploy v3 to export / import into the new system and run c:\Windows\System32\inetsrv>appcmd migrate config "Default Web Site/"  to convert to Integrated Mode.

However we encounter some issues as below:

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

Source Error:
Line 675:            }
Line 676:            return dt;
Line 677:        }
Line 678:
Line 679:        public char getPkg_Type1(string pkgCode, string mark_seg)
 
Source File: h:\inetpub\wwwroot\QCI\App_Code\DataAccess\Request\TandooriDAL.cs    Line: 677

Stack Trace:
[NullReferenceException: Object reference not set to an instance of an object.]
   my.com.idt.qci.DataAccess.Request.TandooriDAL.getAssemblyLocation() in h:\inetpub\wwwroot\QCI\App_Code\DataAccess\Request\TandooriDAL.cs:677
   my.com.idt.qci.Web.UserControl.Web_UserControl_ucQCIlot.bind_ddlAssemblyLocation() in h:\inetpub\wwwroot\QCI\Web\UserControl\ucQCIlot.ascx.cs:963
   my.com.idt.qci.Web.UserControl.Web_UserControl_ucQCIlot.Page_Load(Object sender, EventArgs e) in h:\inetpub\wwwroot\QCI\Web\UserControl\ucQCIlot.ascx.cs:35
   System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) +25
   System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +42
   System.Web.UI.Control.OnLoad(EventArgs e) +132
   System.Web.UI.Control.LoadRecursive() +66
   System.Web.UI.Control.LoadRecursive() +191
   System.Web.UI.Control.LoadRecursive() +191
   System.Web.UI.Control.LoadRecursive() +191
   System.Web.UI.Control.LoadRecursive() +191
   System.Web.UI.Control.LoadRecursive() +191
   System.Web.UI.Control.LoadRecursive() +191
   System.Web.UI.Control.LoadRecursive() +191
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +2428

In the source file, the coding part that the error point too as below:

       public DataTable getAssemblyLocation()
        {

            DataTable dt = null;
            try
            {
                dbManager.Open();
                DataSet ds = dbManager.ExecuteDataSet(CommandType.Text, selectAssemblyLocation());
                if (ds != null && ds.Tables.Count > 0)
                {
                    dt = ds.Tables[0];
                }
            }
            catch (Exception ce)
            {
                throw ce;
            }
            finally
            {
                dbManager.Dispose();
            }
            return dt;
        }

We tried both classic and integrated mode in the application pool, however both does not work.

Any ideas what configuration are missing or coding that when wrong?

Thank you.