An annoying issue - I've done a lot of research into this issue, and the best thread I've found is over at Reddit.
I've tried unplugging every USB peripheral except Keyboard/Mouse, uninstalling Microsoft Security Essentials, doing it from a Clean Boot and disabling all network adapters - and it still fails at about 50% of configuring settings.
If anyone's got anymore advice, that'd be great.
I'm running a SSD with a 1TB Hard Disk.
UPDATE (27/09/2015): I've still had no success with this upgrade, even after trying the ISO upgrade.