We’ve all see this classic error message when performing a Windows build ‘Windows could not parse or process the unattend answer file for pass specialize’
The issue here always applies to a problem with the unattend.xml file being processed at the time and it’s recommended to check the setupact.log and setuperr.log in the c:\windows\panther\unattendGC folder to discover what’s going on.
If you can’t access the CMD prompt via a Shift + F10 at this stage then reboot into WinPE and copy the files over to a network share.
I had the problem recently and although the setuperr.log file reported an issue with the Windows product key the actual issue was caused by the Post Install ‘Configure’ step in a MDT integrated Task Sequence being disabled. This step is used configure the unattend.xml file so if disabled caused this catastrophic effect.
Once re-enabled the problem went away.