My desktop background won't change automatically. OS X 10.6.7 In the Desktop &amp; Screen Saver panel of System Preferences, I check the "Change Picture" box and set it to "Every 30 minutes".

The desktop background doesn't change. 

I tried deleting com.apple.desktop.plist to no avail.
Any ideas?
Thanks for your help,

Damian
You might need to select a new folder of pictures and then back to the pictures you prefer. Deleting one of the plist files not all of them can sometimes leave the preference pane in a state of confusion.

Step one is to get some change, then re-enable the automated change part.