okay so I had the very same problem with my phone. Maddening, I tried and re-tried tried and re-tried, I removed my sim car and tried again, it errored me again, I tried again, finally on another attempt it started to restore software, message read: "verifying software with apple."
message read again: " restoring firmware" and it crashed out again, and at one point no longer even displayed the serial number; came up as "na"
so I reinstalled my sim card and tried it again, thinking it would re-detect something and wouldn't you know it, it failed me again.
haha
I tried it again and wouldn't you know it it bloody worked. I had given up went to finish my laundry with it plugged still and came back to see that it had actually recovered.
bottom line: I HAVE NO IDEA HOW OR WHY!! so with all that I still couldn't give you a quick fix reply. except possibly remove your sim let it totally not recognize it. and try reinserting your sim and see what happens.