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Sounds like the screen saver is set to work from Photo Library. Go to Apple menu > System Preferences > Desktop & Screen Saver.
Click on the Desktop tab at top. Then in left, click Apple section, select Desktop Pictures and select a wallpaper you want.
Then click on Screen Saver tab and top right and select any one there. Then make sure the Source in right is not set to Photos Library. If it is, then change it to something else.
Please let me know if that didn't work, so we can continue troubleshooting.
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