I'm running El Capitan 10.11.6 I get notices that 4 Apple programs have updates to install (iTunes, Safari, El Capitan security update, etc.). In the past the update has always worked. I install them one at a time, usually. Now I can't seem to get them to install. On the update screen, each one has a dark gray button to click to initiate the installation. When I click on the button, the button immediately changes to a light gray color, but nothing else happens. Also no error messages or other helpful information is displayed. Any ideas??