Supplemental results for any site are a disaster. Google's supplemental results are the ones Google keeps in the back file in case the main results can't answer a search query.
And as Google's main results are so great, the supplemental ones don't get used very often.
To check if your site has pages in supplemental results, you can use this search query in the Google search box.
site:www.yoursite.com *** -sjpked
Just substitute yoursite.com for the url of the site you want to check.
If you have pages listed in here, check to see that your navigation links work ok, and start to try to build good pagerank for these pages.