VB linq to entities Field called FIELD_NAME does not exist - vb.net

Question

I have spent the last hours trying to figure out what is causing this exception : Field called GENDER_DESC does not exist. Here are my codes:
Public Class RelationPatient
Public PatNetId As String
Public PatNetIdRel As String
Public Nom As String
Public Prenom As String
Public Sexe As String
Public TypeRel As String
Public Ordre As String
Public DateEnrol As Date
End Class
Public Shared Function GetRelPatient(ByVal PatNetId As String) As List(Of RelationPatient)
Using context As New DAL.SanteReprodEntities
context.Database.Connection.Open()
Dim patient As List(Of RelationPatient)
patient = (From p In context.PAT_REL
Join pa In context.PATIENTS.Include("GENDER_REF") On p.PAT_NET_ID_REL Equals (pa.PAT_NET_ID)
Join pn In context.PAT_NAME On pn.PAT_NET_ID Equals (p.PAT_NET_ID_REL)
Where p.PAT_NET_ID = PatNetId _
And p.VOIDED = 2 Select New RelationPatient With {.PatNetId = p.PAT_NET_ID, .PatNetIdRel = p.PAT_NET_ID_REL, .Nom = pn.LASTNAME, .Prenom = pn.FIRSTNAME, .Sexe = pa.GENDER_REF.GENDER_DESC, .TypeRel = p.REL_TYPE_ID, .Ordre = p.PATIENT_INDEX_TEMOIN, .DateEnrol = pa.ENROL_DATE}).ToList
Return patient
context.Database.Connection.Close()
End Using
End Function
Private Sub FrmLienPatient_Shown(sender As Object, e As EventArgs) Handles MyBase.Shown
DsEnrolement.PAT_REL.Clear()
DsEnrolement.Merge(DAL.dalManager.GetPatRelation(PAT_NET_ID))
Dim patRel As List(Of DAL.RelationPatient)
Dim sexe As String = String.Empty
patRel = DAL.dalManager.GetRelPatient(PAT_NET_ID)
If patRel IsNot Nothing Then
If patRel.Count > 0 Then
For Each rel As DAL.RelationPatient In patRel
MsgBox(rel.PatNetIdRel + ", " + rel.Nom + ", " + rel.Prenom + ", " + rel.Sexe + ", " + rel.TypeRel + ", " + rel.Ordre + ", " + rel.DateEnrol.ToShortDateString) 'This message is displayed well
PATI_RELDataGridView.Rows.Add(New String() {rel.PatNetIdRel, rel.Nom, rel.Prenom, sexe, rel.TypeRel, rel.Ordre, rel.DateEnrol.ToShortDateString}) 'Even if I put any string there like PATI_RELDataGridView.Rows.Add(New String() {"", "", "", "", "", "", ""}) the result is the same
Next
End If
End If
End Sub
Thanks in advance for your help.