Hi again,
which virus scanner do you have on client and server? (Sometimes these cause strange timeouts, so it may be the case in the described situation as well.) Try to disable both temporary and download again.
Would the download work if you try it from within the same LAN (via http://server)? In this case the difficulties could be caused by a bad upload connection to the Internet. Or is this only limited to these file types, and other files (i.e. images or document type files) go through?
Best greetings from Germany
Olaf