Have you tried downloading the program when connected directly to the modem, sans router? Or, even with it being the only thing going through your router at that particular time?
I don't remember when, but I remember seeing something someone wrote about having a large number of devices connected and it was causing problems. It may have just been their particular setup. I don't remember the specifics.
It might be worth a try to be connected directly, for this particular download, at least.