Wizard SDT Property Cannot Be Empty

The 'SDT' property cannot be empty. Define an SDT for the wizard and assign it in this property.

Each wizard, needs to have a Wizard SDT. A Wizard SDT is an SDT that contains data which is shared between steps and that will be used when the wizard is completed.
For more information about this read Defining a Wizard SDT. Set the Wizard SDT in the “SDT” property of the “Wizard” node.

Setting the Wizard SDT in the SDT property of the Wizard node.

After doing this, the main panel can be saved and steps can be added.