Oracle错误：ORA-12541：TNS：打开连接时没有监听器

Question

我有一个webapp，VS2013，C＃和ASP.NET，我使用Oracle 12c作为DB，所以当我尝试从我的webapp连接到DB时，我收到了这个错误：ORA-12541：TNS：没有监听器，这个是我的代码：

  public bool OpenConnection(Label lbl)
    {
        try
        {
            using (cn = new OracleConnection(WebConfigurationManager.ConnectionStrings["RegistroConnection"].ToString()))
            {
                if (cn.State == ConnectionState.Closed)
                {
                    cn.Open();
                }
            }                    
            return true;
        }
        catch (NullReferenceException nullExcept)
        {
            lbl.Text =  "Caught error: ." + nullExcept.ToString();
            return false;
        }
        catch (OracleException dbEx)
        {
            lbl.Text = "OraException - " + dbEx.Message;
            return false;
        }
        catch (Exception ex)
        {
            Exception current;
            current = ex;

            while (current != null)
            {
                current = current.InnerException;
            }

            lbl.Text = "Db base exception - " + ex.GetBaseException().ToString();
            return false;
        }
    } 

我的webconfig上有连接字符串：

  <connectionStrings>
<add name="RegistroConnection"
connectionString="Data Source=(DESCRIPTION =(ADDRESS = (PROTOCOL = TCP)(HOST =myServer)(PORT = 1521))(CONNECT_DATA =(SERVER = DEDICATED)(SID = sidname)));User Id=user;Password=password;"
providerName="Oracle.DataAccess.Client"/>
  </connectionStrings>

已添加的dll是： - Oracle.DataAccess.Client

如果我尝试通过Sql Developer连接，我有一个成功的连接，但在我的webapp上我有这个错误：ORA-12541：TNS：没有监听器