I assume your post under .nbm files for offline install was meant for this thread. It is unfortunate that this problem falls into a category that is difficult for an individual to resolve. If the underlying issue is network related you may encounter failures for downloads from other sites.
In my career I have spent many hours sorting out network problems for my workgroup. In recent time this generally involved careful documentation of the failures that I passed to out IT people, who then worked with the network managers or remote site’s IP people to sort out the problems. Large organizations have been adding layers of security to their networks that often require tweaks to support use cases other than web browsing and Outlook email.