The 1st step is configuring your apache to permit the download of the files you need, for example with the URL http:://localhost/files/err/35854785.err.

Now that you can download, redirecting the file request with

$list->a({-href=>"/files/err/".$file},
          $file)
        );
[download]

This is the simples way to resolve the problem, AFAICS.