I have installed this hack on my test forum, and it works great on 15 out of 20 of my forums.
Of the ones that don't work, all the forum id's are single digit e.g.
http://www.ukgardeningchat.co.uk/archive/5 where the forum id is 5.
However, if I manually type in 05 at the end of the url instead, it works great. eg.
http://www.ukgardeningchat.co.uk/archive/05
but it does not do this automatically. All the forums from 10 upwards are fine. Any suggestions on how to make it work or force the url to read 05?