I am trying to bind an Infragistics Hierichael Web Grid and keep getting the above error message.  When I debug the code, I definately have data in the datasource.  I am not sure where to go from here because everything looks right.  Any help is greatly appreciated.
Here is my code:

protected void Page_Load(object sender, EventArgs e)

         {            

            string physicianNPI;

             decimal mphysicianNPI;

            physicianNPI = Session.Contents["physicianNPI"].ToString();

             mphysicianNPI = Convert.ToInt32(physicianNPI);
           
            var InboxResult = from patientdata in dc.Patients            

                                          join referrals in dc.Referrals on  patientdata.MPI equals referrals.MPI
                                          orderby patientdata.Lname

                                           orderby patientdata.Fname
                                          select new

                                           {referrals.RefDate,

                                               patientdata.MPI,

                                               patientdata.Fname,

                                              patientdata.Lname,

                                              patientdata.DOB,

                                              referrals.RefReason,                                              
                                          };
                       

            WebHierarchicalDataGrid1.DataSource = InboxResult;

             WebHierarchicalDataGrid1.DataBind();             < -----------------  Error Occures Here
        }