Yes, just about all of us at one time or another get a "Duplicate Content" message! No worries; easy to fix!
From a HubPages perspective "Duplicate Content" means that something significant in your Hub is already posted on the Internet somewhere else!
I run into this because I do book reviews! If I put too many quotes in my Hub from the book I am reviewing, even with the authors permission, I am tagged for "Duplicate Content!"
Go back and look at your Hub from that perspective and I bet it jumps right out at you!
If not, sometimes there is an error and HubPages is happy to review it!
Hope that helps! Blessings always, Earth Angel!