I found a temporary solution, I replaced the following code in functions.php
function dedo_download_link( $id ) {
return home_url( '?ddownload=' . $id );
to
function dedo_download_link( $id ) {
return ( 'http://myoldsite.com?ddownload=' . $id );
This works, but I would like to be able to have a mixture of internal downloads and external downloads in the future.