Can't find FULLTEXT index matching the column list

[SorentoUltimate]

Hi when the RSS Cron Run i recieve a Database Error
Database error in vBulletin 3.8.7:

Invalid SQL:

SELECT thread.threadid, MATCH(thread.title) AGAINST ('Πωλήσεις Απριλίου: Πτώση 18,1%') AS score
FROM thread AS thread

WHERE MATCH(thread.title) AGAINST ('Πωλήσεις Απριλίου: Πτώση 18,1%')
AND thread.open <> 10


LIMIT 5;

MySQL Error : Can't find FULLTEXT index matching the column list
Error Number : 1191
Request Date : Saturday, May 7th 2011 @ 05:00:10 PM
Error Date : Saturday, May 7th 2011 @ 05:00:31 PM

That Start happen after i backup my database and restore to a new one.

I Check threads table and the FULLTEXT Index exist with name title and Field title.

Please i need your help to solve the problem.