When I try to exapand the tree view of a database schema it complains that I need Oracle version 11.2 even though I know the database is an earlier version. Was working OK up until about a month ago. I can run queries against the data and also view the records in ALL_TABLES.
Also, are you able to upgrade to a newer version of SQL Developer? We've fixed many, many hundreds of bugs since your version of SQL Developer. Should take about 5 minutes including the time ti takes to download the software.