ORA-03113 usually means that the Oracle Server process for the current session has crashed. Can you check if a user trace dump file exist on the database server that corresponds to this ORA-03113 error? Usually you will see an ORA-00600 error here, with some error codes that may help us find the cause of the problem. If it does, can you send it to me?

ORA-12170 might indicate an idle time-out issue. You could implement aa keep-alive function in your application (e.g. perform a "select * from dual" periodically when the application is idle) or check if a firewall or other network component might kill idle network sessions.