i try to create DataRelation and get error

here my code:
vb.net Code:
  1. Public Class Form1
  2.     Dim ds As DataSet
  3.  
  4.     Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
  5.         ds = New DataSet
  6.  
  7.         Dim dt As New DataTable("dtCustomer")
  8.  
  9.         Dim fid As New DataColumn("id", System.Type.GetType("System.Int32"))
  10.         Dim fkd As New DataColumn("kode", System.Type.GetType("System.String"))
  11.         Dim fnm As New DataColumn("Name", System.Type.GetType("System.String"))
  12.         Dim fkel As New DataColumn("idkel", System.Type.GetType("System.Int32"))
  13.  
  14.  
  15.         ' field properties
  16.         fid.AllowDBNull = False
  17.         fid.AutoIncrement = True
  18.         fid.AutoIncrementStep = 2
  19.  
  20.         fkd.AllowDBNull = False
  21.         fkd.MaxLength = 5
  22.  
  23.         fnm.AllowDBNull = False
  24.         fnm.MaxLength = 50
  25.  
  26.         fkel.AllowDBNull = False
  27.  
  28.  
  29.         dt.Columns.Add(fid)
  30.         dt.Columns.Add(fkd)
  31.         dt.Columns.Add(fnm)
  32.         dt.Columns.Add(fkel)
  33.         'create primary
  34.         Dim uc As UniqueConstraint = New UniqueConstraint(fid)
  35.         dt.Constraints.Add(uc)
  36.  
  37.         uc = New UniqueConstraint(fkd)
  38.         dt.Constraints.Add(uc)
  39.  
  40.         Dim dtkey(2) As DataColumn
  41.         dtkey(0) = dt.Columns("id")
  42.         dtkey(1) = dt.Columns("kode")
  43.  
  44.  
  45.         dt.PrimaryKey = dtkey
  46.  
  47.  
  48.  
  49.         Dim dr As DataRow
  50.         
  51.         For i As Integer = 1 To 20
  52.             dr = dt.NewRow
  53.             dr.Item("kode") = "A00" & i
  54.             dr.Item("Name") = "SAMPLE KE " & i
  55.             If i Mod 4 = 0 Then
  56.                 dr("idkel") = 1
  57.             ElseIf i Mod 3 = 0 Then
  58.                 dr("idkel") = 3
  59.             Else
  60.                 dr("idkel") = 2
  61.             End If
  62.             dt.Rows.Add(dr)
  63.         Next
  64.  
  65.         ds.Tables.Add(dt)
  66.  
  67.             Dim fkid As New DataColumn("id", System.Type.GetType("System.Int32"))
  68.         Dim fknm As New DataColumn("nmkel", System.Type.GetType("System.String"))
  69.  
  70.         Dim dt2 As New DataTable("dtkelompok")
  71.  
  72.         fkid.AutoIncrement = True
  73.         fkid.AllowDBNull = False
  74.  
  75.         fknm.AllowDBNull = False
  76.         fknm.MaxLength = 50
  77.  
  78.  
  79.         dt2.Columns.Add(fkid)
  80.         dt2.Columns.Add(fknm)
  81.  
  82.         Dim unik As UniqueConstraint = New UniqueConstraint(fkid)
  83.  
  84.         Dim pkk(1) As DataColumn
  85.  
  86.         pkk(0) = dt2.Columns("id")
  87.         dt2.PrimaryKey = pkk
  88.  
  89.         Dim row As DataRow
  90.         For i As Integer = 1 To 3
  91.             row = dt2.NewRow
  92.             row("nmkel") = "Category " & i
  93.             dt2.Rows.Add(row)
  94.         Next
  95.  
  96.         ds.Tables.Add(dt2)
  97.  
  98.  
  99.         'relation 
  100.         Dim dtRelation As New DataRelation("qcustomer", fkel, fkid, True)
  101.         ds.Relations.Add(dtRelation)
  102.     End Sub
  103. End Class
i get error at line
Code:
ds.Relations.Add(dtRelation)
error message :
Code:
These columns don't currently have unique values.