Current version of Yosemite on a Mac Pro 2010. The screen saver starts with "Loading Pictures" then about 1 to 2 seconds after displaying the first picture it quits and goes back to my desktop. This is a problem because the computer is password protected after 15 minutes of the screen saver, thus the computer is not secure. I've repaired permissions, rebooted the computer, quit and restarted the screen saver, and even changed the folder of pictures. This problem started three days ago and there were no new applications or updates applied. Any ideas how to get it back to the way it was?