MySQL error in file: /engine/cache/system/plugins/9b152e400fecec95a9e75f821f6c704a.php at line 1119

Error Number: 1139

The Error returned was:
Got error 'empty (sub)expression' from regexp

SQL query:

SELECT id, date, short_story, xfields, title, category, alt_name, MATCH (title, short_story, full_story, xfields) AGAINST ('Dept. H #21 ') as score FROM dle_post WHERE category regexp '[[:<:]](|20)[[:>:]]' AND MATCH (title, short_story, full_story, xfields) AGAINST ('Dept. H #21 ') AND id != 42350 AND approve=1 ORDER BY score DESC LIMIT 4