Hi,
The error is indeed not as clear as it could be, but sbscooker needs to know where the packages coming with SAT installation are, using --include argument, for instance:
sbscooker.exe "C:\Users\MyName\Documents\Allegorithmic\Substance Automation Toolkit\Sbs\YourSbs.sbs" --includes "C:\Program Files\Allegorithmic\Substance Automation Toolkit\resources\packages"