实现一个简单的用户登陆，数据来自Oracle数据库，代码如下，执行到readOracleDataReader reader = cmd.ExecuteReader()时出错。
单步看过用户名和密码都是正确的，哪里有问题呢？新手求教。

 protected void Button1_Click(object sender, EventArgs e)     {         String username = UserName.Text.ToString();         String password = Password.Text.ToString();         String queryString = "select CZR_MM,CZR_XM from T_BYSQ_BJSH_SKB_CZR where CZR_XM=@UserName and CZR_MM=@Password";         // string connString = "DATA SOURCE=orcl;PERSIST SECURITY INFO=True;USER ID=SCOTT;password=admin";         String connString = ConfigurationManager.ConnectionStrings["ConnectionStringUseOracleClient"].ToString();         OracleConnection conn = new OracleConnection(connString);//连接oracle数据库         try         {             conn.Open();//打开数据库，以便下面的操作             Response.Write("数据库打开成功<br>");             OracleCommand cmd= new OracleCommand();//创建一个OracleCommand对象，以便用它执行一个的语句/存储过程             Response.Write("cmd对象创建成功<br>");             cmd.Connection = conn;             cmd.CommandText = queryString;             cmd.Parameters.Add(new OracleParameter("@UserName",username));             cmd.Parameters.Add(new OracleParameter("@Password", password));             OracleDataReader reader = cmd.ExecuteReader();             Response.Write("执行成功<br>");             Response.Write(reader);             Response.Write("连接成功<br>");         }         catch (Exception ex)         {             Response.Write("连接失败");         }         finally         {             conn.Close();         }    }