Error 1 is usually caused due to a problem in hardware, if your phone worked fine before the update process heating the phone is the only permanent solution. In some rare cases BGA soldering dries up or cracks if your device had survived a fall. To do this you need to open up the phone, remove the motherboard and heat it up using a rework station, this is a very risky process, you should heat it to an extent where you don't melt the BGA completely but enough to reattach the connection to the board. If you heat it too much you you will melt the BGA completely and will have a dead device. I have tried this and resurrected many iPhones with error 1. Its best you don't do this your self instead take it to technician.