Hi John,
From memory there were several - I do not recall others but one which is 100% reproducible is
www.wlug.org.nz/rsh(1)
and the ?nocache option is not making it work for me.
(I may be applying that incorrectly.)

As an extra piece of information - I notice this morning that the URL appears to be trying to draw the page for ssh when I was asking for rsh. 

Hope this helps.
cheers
Graham
=====================================
Message: 2
Date: Sat, 26 Jan 2008 16:26:14 +1300
From: "John R. McPherson" <jrm@wlug.org.nz>
Subject: Re: [wlug] WLUG wiki site errors
To: Waikato Linux Users Group <wlug@list.waikato.ac.nz>
Message-ID: <20080126032614.GA18484@wlug.org.nz>
Content-Type: text/plain; charset=utf-8

{snip}
> Over recent days I have had several of
> ==================================
> Fatal PhpWiki Error lib/CachedMarkup.php (In template 'browse' <
 'html'):257: Error: Pure virtual 
> 

Hi,
do you know which page(s) you were on that caused this? It seems that
a previous version of phpwiki has made some cached pages that the
current version doesn't like, for some reason. If you can figure out
the page again, try it again but add a "?nocache" argument
 to the url
and let me know if that fixes it. If it does, then it's definitely a
problem with phpwiki's own caching, and I guess we can just remove
all the cached pages from the database...

John McPherson