I think I've found the solution after a few years experiencing this problem. It keeps reverting back to Unsaved Theme(WITHOUT WALLPAPER SLIDESHOW). Usually occurs after:
1. I plug out the battery, or
2. reboot, or
3. hibernate, or
4. opening Aero incompatible software(such as Digi Broadband), or
5. sometimes let the laptop opened for too long (>12 hours non stop)
6. no reason, suddenly slideshow is disabled(sometimes while I'm watching movies)
I tried creating a theme named "Unsaved Theme" to prevent windows to make its own theme. No success.
I don't want to uninstall any of my favorite programs. The main reason we buy a laptop is to install programs, right?
I've tried deleting slideshow.ini & TranscodedWallpaper.jpg. No success.
I tried enable slideshow on battery and on plugged in (power plan). No success.
I don't want to create new account every time this thing happens. I prefer my OWN Account for eternity.
I also don't want to upgrade Windows every times it happens...
I don't want to compare registry files, windows can change these registry whenever it likes, thus not very practical.
Windows keeps creating its own theme file named Custom.theme and emptying the file slideshow.ini.
The trick is to lock these 2 files but allow windows to access it.
1. Create your theme(setting up all appearances, images, screensaver, font, color, slideshow setting, whatever..),
then name it (e.g.: MyTheme)
Make sure it works on the background before proceed. (use 10 seconds delay to ensure that it works)
2. Go to %localAppData%\Microsoft\Windows\Themes
We only concern about these 2 files:
If there is no Custom.theme, duplicate MyTheme.theme then rename it to Custom.theme.
(In my case, I let Windows do her things in creating the unwanted "Unsaved Theme", so annoying)
use Beyond Compare(or other comparing softwares) between these 2 files:
copy all content from MyTheme.theme --> Custom.theme
MyTheme.theme | Custom.theme
DisplayName=MyTheme | DisplayName=Unsaved Theme
Make sure both of the themes contain something similar to these:
Then, save both files.
THEN THE IMPORTANT PART, change Custom.theme ---> Read only (in properties menu)
3. Go to %USERPROFILE%\AppData\Roaming\Microsoft\Windows\Themes
You will find these 2 files:
slideshow.ini-I think where the slideshow data is stored, who knows
TranscodedWallpaper.jpg-current image being displayed on the background
try open the slideshow.ini, it should contain some gibberish characters e.g:
If it's empty, then your slideshow may already been disabled.
THEN THE IMPORTANT PART, change ONLY slideshow.ini ---> read only (in properties menu)
[don't touch the TranscodedWallpaper.jpg. Just let it be]
4. Then you're ready to enjoy wallpaper slideshow without having to worry about it.
Hope this helps.