before starting the Site Sculptor wizard, you should have a page from your site open, This error sounds like it would happen if a page from your site is not open first.
I think if you are using Design Extender, it would be best to post your questions in the design extender forum, but make sure to include that you are using the Site Sculptor portion in your subject line:
Site Sculptor - Rest of subject
or you can post to the individual forums as well, but make sure to include in your message that you are using Design Extender.