I've just been trying to screenshot some webpages and it didn't work. If I minimised safari, it works fine and snapshots the desktop, saving a file to the desktop, but if I maximise Safari and try again it makes the 'camera shutter' noise but doesn't save the file. Same using cmd-alt-s and pasting into a Word document. Any ideas? Running latest official (not beta) version of 10.11.5 and it was working not so long ago.