I haven't had the same error as you, but I have had something similar about it failing to download. I think that might be because I drove away and it was connected to my home WiFi though.
I have managed to register and verify for my Lexus now as the V5 arrived very quickly. The vehicle was registered on the 30th November and I received the V5 on the 2nd December!
Can't see much advantage to registering at the moment though, as there doesn't seem to be that much in the way of connected services right now, and nothing in the "e-store" under the apps section?? Maybe it's too new that they haven't developed anything for it yet?