When trying to run a query generated using Query Builder, the resulting generated query is showing the query as a long comment. e.g.
SELECT /*+ NOPARALLEL( ACCOUNTS.ACCOUNT_FIRSTNAME FROM ACCOUNTS
The query fails with the following error: "ORA-01742 Comment not terminated properly"
Uncheck View | Toad Options | Schema Browser | Data and Grids | "Use NOPARALLEL hint" check box.
This issue was fixed in version 9.1. The latest version of Toad for Oracle can be downloaded here.