Confused about this, I decided to download the plugin from the WordPress site directly, and put it onto my server via a FTP client software package. The plugin now appears in my plugin page, however it is deactivated. When I click the "activate" button, I get a strange 404 error from my server. I am not having this problem with any other plugin, and have installed a few other plugins since. I've also tried to download and activate this plugin on separate days but still don't work, so I don't think this is a temporary issue. Any ideas? I've never seen this problem before!