Originally Posted by Alrik Fassbauer
I was at the site ca. 5 minutes ago, and out of nowhere Foxit Reader (my replacement for Acrobat Reader) popped up an error message saying : "Not a PDF or corrupted."

Yeah, you should turn off all unneeded plugins that embeds in webpage under Firefox -> Addons -> Plugins. In Internet Explorer it's Control Panel -> Internet Options -> Programs -> Manage Addons -> Toolbars & Extensions (notice how much further you must dig ). I personally use SumatraPDF which is very lightweight.