If it always stops at 99%, I don't know what that could be. But if it stops at different percentages, my guess would be that it is your router or internet provider. With the router you can try to unplug it and then plug it back in again. There is not much you can do about the internet provider.
For big downloads you can get free download software on the internet that will use several threads to accomplish the download. When one of the threads gets stopped for some reason, it will restart it and take up where it left off.
Several months back I spent several hours trying to download a 100mb file. Something with my internet provider (cable) would cause the download to stop at different places and then I would have to start all over again. I found a free file downloader on the internet, installed it, and it was able to download the file the first time.