MySQL error in file: /engine/modules/show.full.php at line 1250

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, tags REGEXP '[[:<:]](Prima guerra mondiale)[[:>:]]' as score FROM if_post WHERE tags REGEXP '[[:<:]](Prima guerra mondiale)[[:>:]]' AND id != 80 AND approve=1 ORDER BY score DESC LIMIT 20