There could be a few problems. You don't have the internal storage space needed for the download (which could be up to twice the size of the file you're downloading). (The phone has only 16GB of storage, about half of that is used by Android and some of the rest of it by hidden files, so if you have a lot of apps installed, or data stored, you could be running low,) The medium you're using (USB, Wifi, mobile data) can't maintain a sustained long download. You're using mobile data and, although you have enough data allowance, you're allowed to download a lot of small files, but you're blocked from downloading a huge file. Other things I'm probably not thinking of at the moment.