I think that error code is for the overload of downloading request and the servers are just full... so you have to wait until the flow of request is normal. Give some hours to get back downloading.
Also a soft reset never hurts... that could solve the error.
I don't know for sure what exactly is causing this error for you, but i myself had to keep trying for a whole week before getting GDR3 update, for WP8 (last year), before it worked. Sometimes the servers are SUPER hard to access because of all the traffic.
What type of internet connection are you using- wifi/ mobile data/ broadband? What's your connection speed?