SQL error, Biblio module

I usually find 20 or so such errors in the log every day:

Got error 'empty (sub)expression' from regexp query: SELECT DISTINCT n.*, b.*, bt.name as biblio_type_name FROM node n left join biblio b on n.vid=b.vid left join biblio_types bt on b.biblio_type=bt.tid INNER JOIN node_access na ON na.nid = n.nid WHERE (na.grant_view >= 1 AND ((na.gid = 0 AND na.realm = 'all') OR (na.gid = 0 AND na.realm = 'tac_lite') OR (na.gid = 251 AND na.realm = 'tac_lite') OR (na.gid = 252 AND na.realm = 'tac_lite') OR (na.gid = 232 AND na.realm = 'tac_lite') OR (na.gid = 234 AND na.realm = 'tac_lite') OR (na.gid = 250 AND na.realm = 'tac_lite') OR (na.gid = 233 AND na.realm = 'tac_lite') OR (na.gid = 280 AND na.realm = 'tac_lite') OR (na.gid = 236 AND na.realm = 'tac_lite') OR (na.gid = 376 AND na.realm = 'tac_lite') OR (na.gid = 240 AND na.realm = 'tac_lite') OR (na.gid = 241 AND na.realm = 'tac_lite') OR (na.gid = 242 AND na.realm = 'tac_lite') OR (na.gid = 246 AND na.realm = 'tac_lite') OR (na.gid = 247 AND na.realm = 'tac_lite'))) AND ( (b.biblio_keywords RLIKE '' ) AND (n.type='biblio' ) AND (n.status = 1 ) ) ORDER BY SUBSTRING(LTRIM(b.biblio_authors),1,1) desc, b.biblio_year DESC LIMIT 0, 25 in /drupal/includes/database.mysql.inc on line 172.

It seems it has got something to do with the biblio module. I'm using drupal 5.10.