In the SQL optimization window in TOAD, when you choose to alter the result view to -> 'CPU Used' the following error appears:
'Could not convert variant of type (Null) into type (OleStr)'
This happens if the Windows regional settings are set to Turkish. If they are set to English, there is no error.
WORKAROUND:
Set Regional Settings to English.
STATUS:
Waiting for fix in a future release of Toad for Oracle