Then reboot, and with any luck it should work to kill that error message once and for all. It certainly did for me. And if you then want to change the drive letters back to what they were, do so by all means - but at your own risk, in my view if it ain't broke don't fix ...
When you unplug your laptop from the AC power, the desktop background slideshow feature will be disabled by default. If you want to preserve the slideshow wallpaper in the background, you need to change advanced power settings. Find the "On Battery" option under the expanded "Slideshow" ...