After version upgrade from 8.6 to 9.0, the following Toad error message was received once the database connection was completed:
"The PL/SQL language parser must have a rule named 'Toad_UserViews'. Please correct this on the Editor-Behavior options page."
Incompatibilities of files between the two versions.
Reboot PC after the upgrade installation.
Locate SettingsLocations.ini file under C:\Program Files\Quest Software\Toad for Oracle folder and rename if to SettingsLocations.OLD. This file may have path to Settings and Options of Toad that is different than the User Files under the default folder to Toad for Oracle. This path may have files that are incompatible with the new version of Toad.