MySQL error in file: /engine/modules/catarchive/main.php at line 113

Error Number: 1139

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

SQL query:

SELECT MIN(YEAR(date)) AS min_year FROM sht_post WHERE category regexp '[[:<:]](|1|18|14|21|15|16|17|9|20|19|2|3|4|5|6|7|8|10|11|12|13)[[:>:]]' AND approve=1