VS10连接Oracle的问题："Oracle.DataAccess.Client.OracleConnection"的类型初始值设定项引发异常.

问题补充：using Oracle.DataAccess.Client; 已经成功引用
private void btnTestConnections_Click(object sender, EventArgs e)//按钮事件
        {
            string connectionString = "Data Source=XXXX;user=XXXX;password=XXXX";//连接字符串正确
            OracleConnection oc = new OracleConnection(connectionString);
            oc.Open(); 
            string sql = "select * from goodsbase where GBID='00901002'"; 
            OracleCommand ocom = new OracleCommand(sql, oc);
            OracleDataReader reader = ocom.ExecuteReader();
            string a = "";
            if (reader.HasRows)
            {
                if (reader.Read())
                {
                    a = (string)reader["GBID"];   
                }
            }
            this.lblLastGenerationDate.Text = a;
           
            reader.Close();
            oc.Close();
        }运行起来，当我单机按钮时报此异常。