OK I tried all the things that everyone posted here too. No luck with any of them.
I also spoke to Applecare a few times, followed their advice to reset a few things and reinstall Aperture, then reinstalled Mountain Lion - all with no luck.
So then I tried creating an album with one photo in it - the screensaver worked.
I then added one image at a time from my 5 star smart album and retested the screen saver each time. It all worked.
Eventually I added a movie. This stopped the screensaver from loading.
So it seems for me that if the album has movies in it, the screensaver breaks.
I now have a smart album that filters out movie files and everything is fine.
Alas this doesn't work for me.
Picture screen saver hasn't worked properly since the Lion upgrade
I've tried the 1 picture approach above (and checked no videos in my folder) but no difference.
Even the initial load up of the preferences doesn't work properly - I call up preferences -> desktop & screensaver and it takes hours even to populate the list of sources to choose photos from. They do eventually load - and I can choose from Aperture folders - but I've long given up on that. So now I choose a file system folder - but even with one photo in, I just get a blank screen with Loading... on for a very long time (last time I checked after an hour the screen was still the same).
Used to work fine - but Apple broke it and I'm surprised they haven't twigged and fixed it - photo screensaver isn't rocket science.
I have this same problem with a new rMBP 2.16 i7. I put my user account on the new Mac from a TimeMachine backup. The admin account on this rMBP is fresh. The photos from any source selectable don't load for the user account. I tried the screen saver from the clean admin account and it worked just like it should. I've deleted the user account plist and lockfile prefs to no effect. I'm reluctant to set up a fresh user account as that is more fuss than fixing a screensaver deserves.
I just tried the same thing: renaming my photo library. I changed my aperture library name from ApertureLibrary to ApertureLibrary_old. Result: Instant loading of the current screensaver photos (National Geographic default ones) when I touch the hot corner. Same with opening the system preferences pane and selecting different screen savers.
This behaviour is reproducible. If I rename the library 'ApertureLibrary' the screensaver hunts for its pictures for a long time. If I change the name to 'ApertureLibrary_old' the photos load without delay.
I put my current user account on my new rMBP using a Time Machine backup. I suspect that the ApertureLibrary.aplibrary permissions might be mangled in some way. Peculiar since I've repaired and rebuilt the Aperture DB since setting up the Mac. Nonetheless, it's a start to fixing this.
Tested this a bit more today. If I load my 'original' 30,000+ library into aperture the screensaver takes forever to load irrespective of its image source. If I create a new library and load in e.g. 1,000 video files and start the screensaver there's no real delay.
I'd like to understand whether the 'forever loading' is a function of the library size or a function of some problem with the library files.
FWIW, I have the similar problems people here are seeing. I have a dozen pics in my iPhoto album, but close to 50,000 in Aperture. Mine usually takes a minute or so to finally load all my options (folders) in the Deskop pref. I *thought* there was a way to NOT share Aperture with the wallpaper system pref, but I don't recall.
It works, but is slow and annoying. This is on a new i5 27" iMac.
My guess is that the Desktop pref needs to rexamine your Aperture library everytime. Bad design, IMO. Or at least offer a way to tell it to ignore Aperture. I just looked, and my Aperture library is 124GB, so that's probably the issue.
*Update - just out of curoiosity, I did as another poster mentioned and renamed my Aperture library, and the 'Desktop' system preference loaded instantly.
Thanks to softwater and all of you for the advice. I did as softwater suggested and the problem persist. On screen saver the option is not usable either. When going to terminal and using:
I get the same thing. With the following code in the terminal :
dyld: DYLD_ environment variables being ignored because main executable (/usr/bin/login) is setuid or setgid
It appears something in /usr/bin/login is creating the problem but hands up for fixing that.
I'm having the same problem, but whenever I open the Desktop & Screensaver system prefs I get alerts avout a network server that can't be found. It's looking for an old, dead machine.
I tried renaming my Aperture and iPhoto Library files and still no luck.
I'm working on a MBP that came with 10.7 installed and I just upgraded to 10.8, but I never used the screensaver before.
By following a suggestion from LeonieDF on another post in this forum, where I had a problem with corruption with my Aperture library, I created a new empty library and then imported my old library into my new library.
I left my Mac and came back to it after a few minutes and saw the screensaver showing the stand photos (that come with Mac) - normally these don't show - I just get Loading... until the screen blanks. So I wondered if it would work for Aperture photos too - and I called up the settings panel, it didn't take very long to populate the list of options, I chose a project in Aperture and again left the Mac for a few minutes - came back and my photos were displaying on the screensaver! Not sure if it will last, but for right now, the screensaver is working as I expect - I've also found my Aperture library is performing faster than before I completely imported it into the new empty library.
I just tried this - taking the originals offline and the behaviour was unchanged.
Despite my 50,000 photo library 120 GB with images relocated and 700 GB with images added I got photos appearing in the screensaver within 60 seconds of the screen blanking.
Seems to me like the library import into a new library has acted a big like a disk defrag - the whole Aperture application is performing faster and screensaver has gone from useful/not working to working as it used to.