5.1 V510 Upgrade Issue

I've received notification of a 5.1 upgrade for my V510. Having just done a full factory reset, I expected this to be a quick upgrade. Unfortunately, I'm getting an error during the installation and I'm not sure what might be going on. I had originally been rooted, but have been using stock recovery. I assumed that the factory reset would clear the rooting.

What can I do to determine the underlying error so that I can attempt to fix it.

Thanks,
Craig