So I spent the afternoon doing some research on this matter [on my phone], and learnt that it isn't the network admin who has blocked the site. The so called security software, Blue Coat, in this case, tags the Commons as Media download site. So blocking sites in this category, blocks Commons, Flickr, YouTube, Vimeo, MetaCafe, etc. Similarily, there are some which categorise the Commons as 'Pornography' ...