Might be corrupted preferences ...
Open the Finder. From the Finder menu bar click Go > Go to Folder
Type or copy paste the following:
Click Go then move the com.apple.systempreferences.plist file to the Trash.
Restart your Mac. See if that made a difference.
Bad Luck fellow Mac -ers, under Mac OS X Mountain Lion ( to quote from "OS X Mountain Lion - the Missing Manual", page 352):-
" Note: You can no longer install different screen-saver styles. And you no longer have a choice of different presentations for you own folders, like the amazing Collage mosaic (which built up one giant photo by using hundreds of smaller photos as individual pixels."
I find this type of functional curtailing of our cherished OS X by faceless Apple apparatchiks quite sinister. It generates echos of "MAD" magazine's Spy Vs Spy scripts, albeit without the humour. I had always believed the people at Apple valued the interlect of their users and revelled at possibilities to stimulate our cerebral processors. Perhaps I was somewhat "glossy eyed" OR we may have been infiltrated by our OS opposition. Beware !!
Interestingly, being a Dr. Who nerd, I downloaded a free, 32 bit screen saver application (Dr. Who Screensaver) from a BBC site which I WAS ABLE to add to the relevant System/Library/Sceen Savers folder. I could then select that screen saver in "System Preferences/Desktop and Screen Saver/Slideshows" which then loaded when scheduled BUT it flickered on screen with a message that a later version was required.
As the screen saver was free, I felt sure that the BBC sources would not be interested in updating the codes (or as may be) so I could run their screen saver on my beloved iMac. I'll try contacting the copyright owners Screentime Media for further help.
The point is - according to the Manual, I SHOULD NOT HAVE BEEN ABLE to get as far as I did. Does anyone have any thoughts, please?
I hope this helps.
Adove is BS post, don't bother reading.
Having the same problem with 10.8.4. I don't have the file that Carolyn mentioned either. I can set the corner to something else, then set it back to sleep and it works that one time, then it will stop working again. I'm very surprised this is happening on my $2700 3 month old machine. My PC using friends are laughing at me and I have to admit this is ridiculous.
If anyone can post any actual suggestions, they'd be appreciated.