catsearch does not support functional invocation??

[spook007]

I'm trying to run the following query...

SELECT ARTICLE_ID FROM ARTICLE
WHERE
(CATSEARCH(ARTICLE_NAME,'ACCOUNTING FINANCE',NULL)>0) OR
ARTICLE_ID IN
(SELECT ARTICLE_ID FROM ARTICLE_KEYWORD
WHERE (CATSEARCH(KEYWORD,'ACCOUNTING|FINANCE',NULL)>0)
GROUP BY ARTICLE_ID HAVING COUNT(ARTICLE_ID)=2)
ORDER BY ARTICLE_ID ASC;

when I run it I get the following error...
SELECT ARTICLE_ID FROM ARTICLE
*
ERROR at line 1:
ORA-20000: Oracle Text error:
DRG-10849: catsearch does not support functional invocation
DRG-10599: column is not indexed

When I run the subquery alone, it works fine as well as the main query. When I join them like I have above, I get the error message. I don't understand what "functional invocation" means, but I'm guessing that CATSEARCH does not support subQueries? If anyone has bumped into this or has any suggestions please post a message!