Npgsql连接PG数据库报错

/// <summary>

        /// get dataset

        /// </summary>

        /// <param name="strSQL">(string)</param>

        /// <returns>(DataSet)</returns>

        public static DataSet Execute4Ds(string strSQL)

        {

            NpgsqlConnection myCn = new NpgsqlConnection(strPostgreConn);

            try

            {

                LogManage.LogError("open connection begin ");

                myCn.Open();

                LogManage.LogError("open connection success");

                NpgsqlDataAdapter sda = new NpgsqlDataAdapter(strSQL, myCn);

                DataSet ds = new DataSet("ds");

                sda.Fill(ds);

                LogManage.LogError("fill ds");

                return ds;

            }

            catch (NpgsqlException e)

            {

                LogManage.LogError(e.Message);

                throw new Exception(e.Message);

            }

            finally

            {

                myCn.Close();

            }

        }

Npgsql连接PG数据库报错：
The type initializer for 'NpgsqlTypes.NpgsqlTypesHelper' threw an exception.