Visual Basic.NET - Error en la llamada a una fución

Public Function MaximoReg() As Integer

    Try

        Dim retorno as Integer

        Dim cmd As New MySqlCommand

        cn.Open()

        cmd = New MySqlCommand("reg_max_calles")

        cmd.CommandType = CommandType.StoredProcedure

        cmd.Connection = cn

        Dim dt As New DataTable

        Dim da As New MySqlDataAdapter(cmd)

        da.Fill(dt)

        'Lo que se debe hacer en este paso es recorrer el datatable y obtener el dato

         For Each row As DataRow In dt.Rows

               retorno = Cint(CStr(row("NombreCampo")))

         Next

        Return retorno

    Catch ex As Exception

        MsgBox(ex.Message)

        Return Nothing

    Finally

        cn.Close()

    End Try

End Function

Dim DataTable dt as new DataTable()

Dim retorno as Integer

dt = MaximoReg("Id", "Gestion", cn)

For Each row As DataRow In dt.Rows

    retorno = Cint(CStr(row("NombreCampo")))

Next

txtId.Text = CStr(retorno + 1)