Because the download is referenced by the fixlet, the Server will attempt to download it and will show progress in the Console, even if the download is no needed by you specific client.
This error is likely caused by a network interruption such as a firewall or proxy blocking the download. It would be unusual for that to work from a browser but not from the root server, but it’s not unheard-of as a firewall/proxy may include the browser’s User-Agent header as part of its rules definition.
You should check with your firewall/proxy admins to fix the problem.
For a quick workaround, you might manually cache the file. Download it via browser, rename it to match its sha1 hash value, and copy it to your server’s wwwrootbes/bfmirror/downloads/sha1 folder.