Link now public, sorry. Meanwhile I will check the article but it looks OK. I have just installed the plugin on my test server and the gallery works there. An I have just uploaded all those files to the main server in case something got deleted - no change. I have checked the DB jos_plugin and they are the same.
<p>{gallery}memories/FamilyLife/large{/gallery}</p> (in the article).
PS Where the gallery DOES work the li class is "sig_block" and where it DOES NOT work the class is "sig_clr". Is this a clue?
<li class="sig-block">
<span class="sig-link-wrapper">
<span class="sig-link-innerwrapper">
<a href="http://192.168.1.64/acdor/images/stories/memories/FamilyLife/large/familyFH28RopeWalksBridport.jpg" class="sig-link" style="width:150px;height:100px;" rel="lightbox[gallery90ed8ec1a4]" title="full text here<br /><br />" target="_blank">
<img class="sig-image" src="http://192.168.1.64/acdor/plugins/content/jw_sigpro/sigpro.transparent.gif" alt="Click to open image!" title="Click to open image!" style="width:150px;height:100px;background-image:url(http://192.168.1.64/acdor/cache/jwsigpro_cache_47b0bd65b6familyfh28ropewalksbridport.jpg);" />
<span class="sig-pseudo-caption"><b>Gallery photo</b></span>
<span class="sig-caption" title="Gallery photo">Gallery photo</span>
</a></span></span></li>