New answers tagged screensaver
Install SmartSleep(from Apple Store) with Insomnia plugin and your problem should be solved. You can even play music with your lid closed with no problems.
I have a Mac Book Pro running 10.9.5. To keep it from sleeping when I locked the screen, I changed the Energy Saver settings for Power Adapter, I checked "Prevent computer from sleeping automatically when the display is off" and I unchecked "Wake for network access".
Quit System Preferences. Locate the relevant plist in terminal by ls ~/Library/Preferences/ByHost/com.apple.screensaver.*.plist You should see something like /Users/<username>/Library/Preferences/ByHost/com.apple.screensaver.0B39A0DE-D1EE-59FF-85C0-6EA16FCB015B.plist Note that hyphen-delimited alphanumeric string. It might be host dependent, ...
Is your machine a member of an Active Directory domain with a group policy set to have the screensaver work in a certain way? Where I work they have policies for such things, as well as proxy settings that break Yosemite. It may be (if you are similarly tied to Active Directory) that you could have something similar going on.
How often does it revert, once an hour? Once a week? Could there be a corrupt photo, or non-photo file in the folder? Maybe try and simplify the folder with just a couple photos, see if it still reverts, and slowly add a few more pics over the course of a few days and see if it continues. You could also try and move the com.apple.screensaver.plist ...
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