The error dialog that you showed might indicate a query that Toad is running which it expects you to have privileges for.
If you turn on Spool SQL (Main Menu -> Session -> Spool SQL -> Spool to Screen), Toad will show you every query that it runs. You can use that to find which query is causing the error (just search for ORA- in the result). Turn that on and let us know what query causes the error.