I had faced this problem and I had contacted with Microsoft customer care and sony vaio but unfortunately no one able to fixed this error
suddenly one option clicked in my mind and I took another internet service provider's modem from my friend and tried to download windows 8.1 surprisingly download started I was too happy but the downloading was too slower than my internet provider so after
so much irritation from speed I disconnected internet and put back my own modem and connected to internet and tried to download windows 8.1 and interestingly my downloading started from where I left downloading,
so I would like to advice try with another internet service provide, all the best