Downloading source documents uses wget, which comes installed with Greenstone.

If you are trying to download behind a proxy server, you'll need to set the http_proxy environment variable:

export http_proxy=http://www.proxyaddress.com
or 
set http_proxy=http://www.proxyaddress.com

Then, create or open the file .wgetrc in your home directory, and add the following lines: 
proxy_user=username
proxy_password=password