I had the same problem, and I am NOT using remote desktop. My copy command is not working from de sql window, comand window, explaint plant window etc.. It just work from de result of a SQL (sql window), but just in the result table. Also I can do a copy command from other program and do a paste command in PlSQlDev. But not do a copy command, it works sometimes (eventually). That started when I wast testing de version 9. After that I had desinstalled a couple of times, and also the last time I also erased every file and register record about Pl/SqlDeveloper before to re-install. But, nothing ... the copy just work when it want... and most of the time NOT.