|Aha. Seems I was not aware of the subtlety of "Internet Explorer Wallpaper",|
so I'm glad timmycb came along.
Well then, if it is in the location given in #4 then probably you are not set to show hidden files and folders. The folder Application Data is hidden.
Go to Control Panel > Folder Options > View.
Put the blob in "Show hidden files and folders".
Untick "Hide extension for known file types" too.
Apply/OK your way out.
I would recommend you keep these settings anyway.
If you now follow the advice in #4 you should find your file. You will have to carry out the above procedure on the other machine when you move it over and if necessary create any missing folders.
Google is NOT the only Search Engine!