After upgrading my app to Rails 3.1, I found that admin_data had some issues. Specifically with the parent_layout helper method and serving up the public files.
This is a quick and dirty fix to get things working. Eventually the assets should be redone to support the asset pipeline in 3.1. But this should get things working for now.
Fixing Rails 3.1 compatability for public#serve
Rails 3.1 compatability fix for the parent_layout helper