phpBB forum error, HELP!

SQL Error : 1016 Can't open file: 'phpbb_search_wordmatch.MYI'. (errno: 145)

INSERT INTO phpbb_search_wordmatch (post_id, word_id, title_match) SELECT 5766, word_id, 0 FROM phpbb_search_wordlist WHERE word_text IN ('particularly', 'great', 'passable', 'tho')

Line : 251
File : functions_search.php

People are getting this everytime they post, what does it mean, and how is it fixable? the post still goes ahead fine, but the 'last post by' bit is wrong

HELP!!!