Here's the fix:

1) Close all windows & apps
2) Go to the System Library by selecting Finder, the hold the Option Key, then click on the Go tab at the top
3) Open the Application Support folder
4) Open the Dock folder
5) You should see desktoppicture.db in the Dock folder
6) Drag the desktoppicture.db to Trash
7) Reboot and you should be Good-To-Go

今天也遇到了和这个问题，在苹果官方论坛找到的解决方案。