I made this ISO with 2 stages. 1. I added lots of stuff (tweaks, applications, etc and it worked). 2. I tried to make it fully automated (and here is the problem). In my opinion, the source of the problem is in winnt.sif: [Unattended] UnattendMode=FullUnattended; <------- Problem UnattendSwitch="Yes" OemPreinstall="Yes" OemSkipEula="Yes" FileSystem=* WaitForReboot="No" NoWaitAfterTextMode=1 NoWaitAfterGUIMode=1 DriverSigningPolicy=Ignore NonDriverSigningPolicy=Ignore Please note the marked line. I think I haven't supplied enough information for it to be fully automated.. I used nLite again and made it fully automatic with it and then there where no error messages. Because I Re-edited using nLite it deleted some of my modifications, so it's not a good solution, but at least I know that it's fixable without starting all over again. What do you think?