Hi!
I had the same (I wasn't fast enough to capture it though) for one of the feeds I added (Slashdot)...
Funny thing is that it was complaining about Slashdot but it displayed it, it was the "Inside the Asterisk Feed" it was unable to display when I had that error message (as if it somehow confused the two and was complaining about a duplicate key because of that)...
This was with FreePBX 13 for me...
Have a nice day!
Nick