We have the same problem. When you remove the <Copyprofile> from your unattend.xml, it probably will work, but you'll have problems with the profiles (settings)
On the internet more people have this problem, seems to be a Win 7 bug. There are ways to work around it by editing the registry when sysprepping your image.
See also this link for a possible solution.
Yeah, I had found that same article and it was the correct issue. Once I changed the profile setup to only have the local administrator, everything transferred properly.