I have just managed to fix a phone with an Error 50 on it. NONE of the help on this forum helped so what i did was this. I held down the Home Button and Power Button for 10 seconds whilst the phone was connected to my Mac. I then let go of the Home button BUT I KEPT HOLDING THE POWER BUTTON during the whole of the sync process and hey presto it worked. Yes i had a sore finger by the end but it has been 2 weeks and my phone has been in 3 shops who couldn't fix it INCLUDING the Glasgow Apple shop. Hopefully this will work for you guys as well.