Check also the files on the root on X: drive. There are there the unattended.xml generated file, and the batch used, and the log of the unattended also if I remember well.
We do have the same problem, the default unattended failed, and must use a custom one to make it works. We open and create a Symantec case for that, and provide all the logs (was the case 414-725-599)
But finally, we were not able to test again after deploy the latest SP1, so the Ticket auto-closed, never solved... We use the workaround of a custom file.