The setwallpaper command (I never use) must still working but check out your syntax

The IF command must ended by ENDIF perhaps the troubles come from this.

For writevalue ("HKEY_CURRENT_USER\Control panel\Desktop","adtaker.bmp" "REG_SZ") ckeck the syntax too. There is a missing "entry" parameter and a missing "," between "adtaker.bmp" and "REG_SZ"

The command line must be
writevalue ("HKEY_CURRENT_USER\Control panel\Desktop","Wallpaper","adtaker.bmp","REG_SZ")

Hope this helps and solve your problem

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Comments always welcome.
French native so I apologize for my (mis)use of English!