MySQL Error

Error Message:
Illegal argument to a regular expression.
Error Number:
3685
SQL Query:
SELECT id, autor, date, short_story, SUBSTRING(full_story, 1, 15) as full_story, xfields, title, category, alt_name, comm_num, allow_comm, allow_rate, fixed, rating, vote_num, news_read, votes, flag, editdate, editor, reason, view_edit, tags FROM dle_post WHERE category regexp '[[:<:]](15)' AND approve=1 AND date < '2026-05-13 02:13:12' ORDER BY fixed desc, date DESC LIMIT 0,10