运行程序时出现了 ORA-12154: TNS: 无法解析指定的连接标识符解决方法

运行程序时出现了 ORA-12154: TNS: 无法解析指定的连接标识符
源代码如下:
using System;
using System.Collections;
using System.ComponentModel;
using System.Configuration;
using System.Data;
using System.Data.OracleClient;
using System.Drawing;
using System.Web;
using System.Web.Security;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Text;

public partial class _Default : System.Web.UI.Page
{
  protected void Page_Load(object sender, EventArgs e)
  {
  string sConfirmCode;
  this.Title = "欢迎光临XXXXXXX中心";


  if (!IsPostBack)
  {
  if (Session["UserID"] == null)
  {
  LabelWelcome.Text = "欢迎光临，请先登陆";
  }

  //增加了创建验证码得代码 2007－3－1 congcong
  sConfirmCode = GetConfirmCode(5);
  Session["ConfirmCode"] = sConfirmCode;
  Image1.ImageUrl = "ImageConfirmCode.aspx";
  // 增加代码结束 2007－3－1 congcong
  }
  }
  protected void ButtonLogin_Click(object sender, EventArgs e)
  {
  string sUserID, sPassword, sUserName, sUserLvl, sCompany;

  //增加了对于验证码得判断 2007－3－1 congcong
  string sConfirmCode,sSessionConfirmCode;
  sConfirmCode = TextBoxConfirmCode.Text;
  sSessionConfirmCode = Session["ConfirmCode"].ToString();
  if (sConfirmCode != sSessionConfirmCode)
  {
  Response.Redirect("错误报告.aspx?ErrorCode=验证码输入错误！请返回，重新输入");
  }

  // 增加代码结束 2007－3－1 congcong

  sUserID = TextBoxUserID.Text;
  sPassword = TextBoxUserPassword.Text;

  LabelWelcome.Text = sUserID;
  string sConnectionString, sSelectCommand;

  sConnectionString = ConfigurationManager.ConnectionStrings["OraConnectionString"].ConnectionString;
  OracleConnection MyConnection = new System.Data.OracleClient.OracleConnection(sConnectionString);

  sSelectCommand = "scott.P_CHECK_USER_PASSWORD";
  OracleCommand MyCommand = new OracleCommand();
  MyCommand.Connection = MyConnection;
  MyCommand.CommandText = sSelectCommand;
  MyCommand.CommandType = CommandType.StoredProcedure;

  MyCommand.Parameters.Add("vUserID", OracleType.VarChar).Value = sUserID;
  MyCommand.Parameters.Add("vUserPassword", OracleType.VarChar).Value = sPassword;
  MyCommand.Parameters.Add("vUserlvl", OracleType.VarChar, 1).Direction = ParameterDirection.Output;
  MyCommand.Parameters.Add("CountUser", OracleType.Number).Direction = ParameterDirection.Output;
  MyCommand.Parameters.Add("vUserName", OracleType.VarChar, 20).Direction = ParameterDirection.Output;
  MyCommand.Parameters.Add("vCompany", OracleType.VarChar, 20).Direction = ParameterDirection.Output;

  MyCommand.Connection.Open();
  MyCommand.ExecuteNonQuery();

  if (Convert.ToInt32(MyCommand.Parameters["CountUser"].Value) == 0)
  {
  Response.Redirect("错误报告.aspx?ErrorCode=5");
  return;
  }
  else if (MyCommand.Parameters["CountUser"].Value == null)
  {
  Response.Redirect("错误报告.aspx?ErrorCode=6");