I changed the file extension from .wbt to .wbt_at and I still get black wallpaper instead of the desired wallpaper image.
I also tried a .wbt_af extension will the same undesirable results: a black wallpaper.
screen.
I also complied .exe with "highest available" and did a right click on the .exe file.
Then I chose run as Admin and still the same result. It just does not work for me, yet.
I yearn for a solution to this wallpaper background solution.

:'(
Here is the code:
;changewallpaper.wbt_af
;changewallpaper.wbt_at
;changewallpaper.wbt
;If you want to run an uncompiled script as an elevated admin,
;change the file extension from ".wbt" to ".wbt_at" or ".wbt_af".
DirChange("f:\Creating Power Habits")
a = FileItemize("*.jpg")
a = AskItemlist("Select New paper", a, @TAB, @UNSORTED, @SINGLE, @FALSE)
TILE = @FALSE
If FileSize(a) < 40000
TILE = @TRUE
pause("TILE lesson thatn 40000",TILE)
else
pause(a,"file size 40000 or more")
endif
Wallpaper(a, TILE)
pause("Done","hahaha")