The accounting has already been done for that Aug 25, 2007 invoice and it will not be reversed by processing the new invoice. All that will really get affected is that this invoice cannot be re-printed, or appear on reports based on OrderEntry History.

If you use Adagio SalesAnalysis, the new invoice may not be retrieved because of the duplicate number. You might have to deal with the old invoice first (archive/purge it).

All this being said, there likely is a better way that OrderEntry can be dealing with preventing the duplicate document number in the first place. An atypical scenario is at the root of this situation, but there is room for improvement.