Andy, I might have your answer. I ask if you could see if Network Services were ended or somehow reset then see if the IPC entries were reset. You might also want to see if a key user ID is being disabled as part of some nightly process (like backups or critical reporting) in order to keep users from signing on.
Could be an issue connecting to the database because of the TNSNAMES.ORA
Copy it from the stand alones CLIENT folder into the (typically) c:\app\administrator\product\11.2.0\client_1\network\admin folder