I have ran into this issue a number of times.
In MDT, I am creating offline media build for deployment via USB drive. I would like to make the deployment as simple as possible. So in the CustomSettings.ini there are lots of Skip syntax.
Whe you use the SkipTaskSequence=YES command the build fails after the wizard with a comment: Invalid DeploymentType “”.
Turns out you can’t use the SkipTaskSequence=YES syntax in the CustomSettings.ini because there is no DeployRoot variable in BootStrap.ini file. Add a DeployRoot in and it works fine (but we dont use one when using offline media, grrr).
Have a look at this social TechNet page, the last entry.