The reason you are getting this error is because you have included a CSS Menu Writer menu in your template. When you are creating a new Site Sculptor design the template and menu are separate components. Here is how you will need to set it up.
Make sure that you have your CSS Menu Writer menu saved as a preset. Next remove the menu from your template. Now with the template not having a menu on it go to the preset manager and make a new Site Sculptor Site Design. When you go through this interface you will first choose the template for the main page, then on the next step you will be able to select your CSS Menu Writer menu preset that you would like to use in the design, then you can specify the orientation and the region that you would like the menu added to.