MySQL error in file: /engine/modules/show.full.php at line 981

Error Number: 3685

The Error returned was:
Illegal argument to a regular expression.

SQL query:

SELECT /*related_ids_2*/ id, date, short_story, xfields, title, category, alt_name FROM dle_post WHERE category regexp '[[:<:]](20019|56)[[:>:]]' AND MATCH (title, short_story, full_story, xfields) AGAINST ('Массовая культура утопии ') AND id != 275555 AND approve=1 LIMIT 12