Nope, not the problem either; all the other tables are using 255, too.
Code:
mysql> describe posts;
+--------------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+------------------+------+-----+---------+----------------+
| id | int(11) unsigned | | PRI | NULL | auto_increment |
| subject | varchar(255) | | | | |
| contents | text | | | | |
| threadid | int(11) | | UNI | 0 | |
| datetime | int(11) | | | 0 | |
| posteruserid | int(11) | | | 0 | |
+--------------+------------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)