Since I upgraded to version 2.8.5 I've had trouble auto-updating plug-ins and couldn't auto-update to version 2.8.6. I'm running two WordPress sites and the problem affects both.
I was looking at an entirely different problem earlier today and noticed port 80 is closed on this PC. A little digging tells me this is the port WP uses to FTP files. Could this be why I can't autoupdate?