We just upgraded to oracle 11G and on some of our very large schemas we are not able to see the database objects. For instance when clicking on the plus sign on the tables nav will popup an hour glass, then just go blank.
The hour glass goes away but we are not able to drill down to the tables. My schema has 831 tables but this should not be a problem. We are able to see the tables in sys which has over 900 tables.