sharepoint 2010 query external list programmatically + Attempted to perform an unauthorized operation.

Hi All,

 i have an external list which is get data from simple SQL table. while viewing the External list work fine. but when i am trying to retrieve the data by CAML Problematically i am getting error 'Attempted to perform an unauthorized operation' .

                    using (SPSite oSite = new SPSite("Site Address"))
                    {
                        using (SPWeb oWeb = oSite.OpenWeb())
                        {

                            SPList oList = oWeb.Lists.TryGetList("External_List_To_test_Linq");
                            SPQuery oQuery = new SPQuery();
                            string camlquery = @"<Where><Eq><FieldRef Name='ID'/><Value Type='Text'>1</Value></Eq></Where>";
                            oQuery.Query = camlquery;

                            SPListItemCollection listItemCollection = oList.GetItems(oQuery);
                            foreach (SPListItem oitem in listItemCollection)
                            {
                                Console.WriteLine("ID" + oitem);
                            }

                        }
                    }

I am getting error while Reading the ID. it says 'Attempted to perform an unauthorized operation'.