I obviously have not seen the screenshot you posted ...but there are certain guidelines you need to follow when submitting one.
The wallpaper in the screenshot itself must be sufficiently obscured by other things, like perhaps having your startmenu show in the screenie, or some strategically placed widgets which would help to obscure a fair section of the wallpaper.
If it is deemed by moderators that someone could extract a wallpaper from your screenshot, it will be rejected as there's the permission issue involved.
If it's a distasteful wallpaper [e.g. nudes, drugs etc] it will also be rejected.
Hope that helps for your next submission. Don't give up ñot everyone succeeds with their first uploads.
