ORA-01012: not logged on
Cause: A host language program issued an Oracle call, other than OLON or OLOGON, without being logged on to Oracle. This can occur when a user process attempts to access the database after the instance it is connected to terminates, forcing the process to disconnect.
Action: Log on to Oracle, by calling OLON or OLOGON, before issuing any Oracle calls. When the instance has been restarted, retry the action.