Error Number : 1191 MySQL Error : Can't find FULLTEXT index matching the column list

[omanmoon.net]

Hello
i am tired from this error

atabase error in vBulletin 4.0.5:

Invalid SQL:

SELECT searchcore.searchgroupid, MATCH(searchcore_text.title, searchcore_text.keywordtext) AGAINST ('test') AS score
FROM searchcore AS searchcore
JOIN searchcore_text AS searchcore_text ON (searchcore_text.searchcoreid = searchcore.searchcoreid)

WHERE MATCH(searchcore_text.title, searchcore_text.keywordtext) AGAINST ('test') LIMIT 500;

MySQL Error : Can't find FULLTEXT index matching the column list
Error Number : 1191
Request Date : Wednesday, September 22nd 2010 @ 04:47:20 AM
Error Date : Wednesday, September 22nd 2010 @ 04:47:20 AM
Script : http://www.###/vb/search.php?do=process
Referrer : http://www.####t/vb/search.php
IP Address : #####
Username : ####
Classname : vB_Database
MySQL Version : 5.1.50

can any one help me pleas

Thanks