Discuz! Database Error

(1064) You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ') and b.first=1' at line 1

select count(*) from forum_thread a join forum_post b on a.tid=b.tid where a.attachment!=0 and a.displayorder>=0 and a.fid in() and b.first=1

PHP Debug

No.	File	Line	Code
1	plugin.php	47	include(%s)
2	source/plugin/forum_index/forum_index.inc.php	22	discuz_database::result_first(%s)
3	source/class/discuz/discuz_database.php	117	discuz_database::query(%s, Array, false, false)
4	source/class/discuz/discuz_database.php	136	db_driver_mysql->query(%s, false, false)
5	source/class/db/db_driver_mysql.php	153	db_driver_mysql->halt(%s, %d, %s)
6	source/class/db/db_driver_mysql.php	224	break()