Though there's no guarantee that this will help, you can try flushing your computer's DNS cache to see if it might help. To do so, first unplug the HughesNet modem. Then, start your computer's command prompt and type "ipconfig /flushdns", without the quotes, and hit enter. And there IS a space between g and /. After the success message, close the command prompt and shut your computer down. Plug in the HughesNet modem, wait at least five minutes, then start your computer and try again.
Again, there is no guarantee that this will help, but it's possible that your system has gotten a faulty DNS address for the Endicia server while using HughesNet and it's causing the problem, whereas the DNS address for Endicia while using alternate internet service may be correct, so it's working the way it should.
It's worth a shot. Again, I don't know if it will help, but I hope it does.