This is an HF3 issue and I would log a support ticket on this but the support site is still broken at the moment.
HF2 worked perfectly and now the unattend.xml has missing information.
It was missing information in the "specialize" pass. I had to add MAC addresses and "true" statements for DHCP in a couple of places.
This got rid of the error message but it tried to log in with the disabled local admin account.
I then noticed that the entire tail of the section which involves creating a local "Ghost" account which then runs the driver installation script was also omitted.
I would advise users to NOT upgrade to HF3 at this time until this is resolved.
EDIT: I should further clarify that the issue only seems to affect a brand new, pre-defined computer. If you instll the agent onto an existing production OS and allow it to upload its basic inventory it can be built correctly, and re-built as well.
However when you add a pre-defined computer with just computer name and MAC address and PXE boot this machine, as soon as the agent connects and is ready to accept jobs you will see the MAC address disappear and the IP address appear in its place. This does not happen to a machine that has been seen in production before.