I have a new 21.5 inch Late 2013 iMac which I have been using for a few days now - replacing the early 2009 iMac I had previously. I have a directory of photos on an directly attached (USB) external drive that I used as my rotating wallpaper on the previous computer. I set the new one to use that directory and to rotate every 30 minutes. Once set it works as you would expect. However, when the computer is turned off and then turned back on, it reverts to the default wallpaper (the one it was using when first taken out of the box) and I have to reset it to my desired location and settings. I had no problem on the old iMac. Anyone have any ideas/suggestions on this?