Str = @"User=" + textBox4.Text + @";Password=" + textBox6.Text +
                                                          @";" +
                                                          @"Database=" + textBox1.Text;
fbConStr = new FbConnection(Str);
                                                        fbc = new FbCommand();
                                                        fbc.CommandText =
                                                            @" update Orders set N15=" +
                                                            dtZag.Rows[curRow][ 3 ].ToString() +
                                                            " where NOrder=" + UID_RM + " and N14=" +
                                                            dtZag.Rows[curRow][ 4 ].ToString();
                                                        fbc.CommandType = CommandType.Text;
                                                        fbc.Connection = fbConStr;
                                                        fbConStr.Open();
                                                        
                                                        fbc.ExecuteNonQuery();
                                                        fbConStr.Close();

attempted update of read-only column