I do not know what might be the cause of this but I can't download Ubuntu 12.10 from their website, it gets stuck on 761 MB.
I disabled avp system and tried to download it with Chrome and Firefox but still it got stuck on 761MB out of 763MB.
Quantal Quetzal 12.10 has just been released. The servers are extremely busy. Added to this, a large number of updates for Quantal have just dropped.
I suggest you try a BitTorrent download.
I've been getting my iso images through the official bitTorrent for a few years now, for several reasons:
Maybe you can try to download it by Torrent system, or choose another mirror. If you prefer the direct download, I recommend to use a download manager (Uget, Steadyflow), so you can pause it.
There is a list of mirrors and torrent links on this site: