A first chance exception of type 'System.Data.SqlClient.SqlException' occurred in System.Data.dll

try
{
      ХарактеристикиБД_TA.Update(ХарактеристикиБД_DT);
}
catch (Exception ex)
{
      SysLOGW("Ошибка при сохранении данных в \"Характеристики БД\": " + ex.Message);
}

Violation of PRIMARY KEY constraint 'PK_Измеренные значения за месяц_NEW'. Cannot insert duplicate key in object 'dbo.Измеренные значения за месяц'.
The statement has been terminated.

foreach ( DataRow dr in myDataTable.Rows ) dr.SetModified ( );

RowState = Added

string sqlTable = ValuesPerMonthDB.TableName ;

                    // Prepare connection
                    SqlConnection connection = new SqlConnection(SarkWinPRG.Properties.Settings.Default.SARKConnectionString);

                    DataTable _table = ValuesPerMonthDB;
                    SqlDataAdapter da;
                    DataTable workTable = ValuesPerMonthDB.Clone();

                    // Get keys for target table
                    String sqlKeys = "EXEC sp_pkeys @table_name = '" + sqlTable + "'";

                    da = new SqlDataAdapter(sqlKeys, connection);
                    DataTable KeyColumns = new DataTable();
                    try
                    {
                        da.Fill(KeyColumns);
                    }
                    catch { }
                    if (KeyColumns.Rows.Count > 0)
                        foreach (DataRow row in _table.Rows)
                        {
                            String sqlCmd = "SELECT * FROM dbo.[" + sqlTable + "] WHERE ";
                            foreach (DataRow keyRow in KeyColumns.Rows)
                            {
                                String colName = keyRow["COLUMN_NAME"].ToString();
                                Type colType = _table.Columns[colName].DataType;
                                if (colType == typeof(String))
                                {
                                    sqlCmd += "[" + colName + "] = '" + row[colName].ToString() + "' AND ";
                                }
                                else if (colType == typeof(DateTime))
                                {
                                    String date = ((DateTime)row[colName]).ToString("u");
                                    date = date.Substring(0, date.Length - 1);
                                    sqlCmd += "[" + colName + "] = CONVERT(datetime, '" + date + "', 102) AND ";
                                }
                                else
                                {
                                    sqlCmd += "[" + colName + "] = " + row[colName].ToString() + " AND ";
                                }
                            }
                            sqlCmd = sqlCmd.Substring(0, sqlCmd.Length - 5);
                            da = new SqlDataAdapter(sqlCmd, connection);
                            try
                            {
                                da.Fill(workTable);    // fill table with old row
                            }
                            catch { }
                        }


                    foreach (DataRow row in _table.Rows)
                        workTable.LoadDataRow(row.ItemArray, false);
                    // Prepare DataAdapter for database update
                    da = new SqlDataAdapter("SELECT * FROM dbo.[" + sqlTable + "]", connection);
                    SqlCommandBuilder cb = new SqlCommandBuilder(da);
                    try
                    {
                        da.UpdateCommand = cb.GetUpdateCommand();
                        da.InsertCommand = cb.GetInsertCommand();
                        da.DeleteCommand = cb.GetDeleteCommand();
                        // Update SQL database
                        da.ContinueUpdateOnError = true;
                        da.Update(workTable);
                    }
                    catch (SqlException e)
                    {
                        SysLOGW("SQL error: "+ e.Message);
                    }
                    catch (InvalidOperationException e)
                    {
                        SysLOGW("The input table is invalid. SQL error: " + e.Message);
                    }
                    catch (DBConcurrencyException e)
                    {
                        SysLOGW("Concurrency error - An attempt to execute an INSERT, UPDATE, or DELETE statement resulted in zero records affected. SQL error: " + e.Message);
                    }
                    catch (SystemException e)
                    {
                        SysLOGW("SQL error: " + e.Message);
                    }