MySQL error in file: /engine/modules/show.full.php at line 978

Error Number: 3685

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

SQL query:

SELECT id, date, short_story, xfields, title, category, alt_name FROM dle_post WHERE category regexp '[[:<:]](3691)[[:>:]]' AND MATCH (title, short_story, full_story, xfields) AGAINST ('Овсяноблин ') AND id != 97820 AND approve=1 AND date < '2024-04-18 06:22:58' LIMIT 6