What is this error message trying to tell me?

Thanks!



select tID, date_format(date, '%m-%d-%Y') as showDate, viewed, summary, MATCH (summary)
AGAINST ('lemon') AS score from testimonies where approved = 'Yes' and match (summary) against
('lemon' in boolean mode) order by score desc limit 50;

Error Code: 1191. Can't find FULLTEXT index matching the column list