PANDA penalizes duplicate content more than anything else. Make sure your Hubs are unique by using Copyscape. (People may have stolen your hubs and placed them on other websites.)
If you have a lot of comments on your Hubs from people outside of Hub pages - with links pointing to external websites, check to make sure that they are not copied from other sites. I had to delete some comments that copied paragraphs word for word from other websites.