Is it possible to set filtering using a specific number of CheckedListBox?

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VB

Because I have 6 CheckedListBox and whenever I select items from 4 CheckedListBoxes only, an error pops up but it still filters.

*UPDATED
(For every CheckedBoxList, this is the code that I use but with different variable names)
And also is there a way to make multiple data into one? Example is, when I input John in Client 4x, it would show John(x4) in the CheckedListBox. But the goal is to filter.. Is there a way to make John appear once?

Dim dt1 As DataTable
      Dim ds1 As New DataSet
      cnn = New OleDbConnection(connectionString)
      Dim clientList As String = "("
      For item1 As Integer = 0 To CheckedListBox2.CheckedItems.Count - 1
          clientList += "'" & CheckedListBox2.CheckedItems(item1) & "',"
      Next
      clientList = clientList.Substring(0, clientList.Length - 1) + ")"

      Dim sql1 = "select * from NTIdb where Client in " + clientList

      Try
          cnn.Open()
          adptr = New OleDbDataAdapter(sql1, cnn)
          adptr.Fill(ds1)
          adptr.Dispose()
          cnn.Close()

          dt1 = ds1.Tables(0)
          Form5.DataGridView1.DataSource = dt1

      Catch ex As Exception
          MsgBox(ex.ToString)
      End Try
      Form5.DataGridView1.Visible = True