When I try to search on the forum, or I click the button to see all posts since my last visit, I get this kind of error:

General Error

Could not delete old search id sessions

DEBUG MODE

SQL Error : 1054 Unknown column 'search_time' in 'where clause'

DELETE FROM phpbb_search_results WHERE search_time < 1153996545

Line : 657
File : search.php

I was hoping it would fix itself but it's been two days now and it's rather annoying.

Ah, phpbb was recently updated but the database wasn't updated along with it. This is now fixed. Thanks.