Error with textbox in VB.Net using autocomplete

I have the following code to perform an autocomplete in several textboxes that I have in my application. It is connected to a database in another computer that is a server. But the error gives me as much of the clients as of the servers.

Taking the issue of sqlinjection out that I know my code is vulnerable, there are times where the code works and moments where it does not.

I clarify that the base is very large and the query I show is just one of the textbox that I will use. The info is taken from a table called employees, and the column is nro_doc.

Public Sub autocomplete (ByVal textbx As TextBox, ByVal table As String, ByVal description As String) Dim cmd As New OleDb.OleDbCommand Dim res As DataTable Dim sql As String=""

sql &= "SELECT top 10 " & descripcion & " FROM " & tabla & " WHERE " & descripcion & " LIKE '" & textbx.Text & "%'"


If conectar() = resultado.ok Then
    Try
        If textbx.Text <> "" Then
            res = acceso.consulta(sql)
            If res.Rows.Count() <> 0 Then
                textbx.AutoCompleteSource = AutoCompleteSource.None
                If res.Rows.Count() <> 0 Then
                    Dim c As Integer = 0
                    For c = 0 To res.Rows.Count() - 1
                        textbx.AutoCompleteSource = AutoCompleteSource.CustomSource
                        textbx.AutoCompleteMode = AutoCompleteMode.Suggest
                        textbx.AutoCompleteCustomSource.Add(res.Rows(c).ToString)
                        'textbx.AutoCompleteCustomSource = res.Item(descripcion)
                    Next
                End If
            End If
        End If

    Catch ex As Exception
    MessageBox.Show("Error al intentar conectar", "Error grave")
    Me.ultimo_error = ex.Message
End Try
End If

End Sub In turn, the method I'm calling from the textbox ChangeText event.

Private Sub txt_nro_documento_TextChanged (sender As Object, and As EventArgs) Handles txt_nro_documento.TextChanged acceso.autocompletar (txt_nro_documento, "EMPLOYEES", "nro_doc") End Sub

And now yes, the error that you are giving me is this:

system.accessviolationexception attempt to read or write to protected memory. This often indicates that there is another corrupted memory.

I searched everywhere but I have not found a solution that suits my problem. I put the textbox because before this did not happen and I think that everything is originating there because when I take out the autocomplete there are no errors.

Thank you, I hope someone can help me, I'm a novice, so you need patience!