G700/S8300 standalone 2410 phones. Customer hits conference calls second party, answers ok, hits conference and confernce doesn't happen..still talking to second party. Can put on hold and toggle back and forth to either but cannot conference them. Internal conference ok but cannot conference 2 outdie. Trunk to trunk transfer is enabled.List trace station shows denial event 1760 COR restriction. Checked and changed most things in the COR with no result. Any ideas??