YES IT IS A ERROR!! ANY COIN IN GENERAL, PENNY DIME,QUARTER,AMERICAN EAGLES SILVER STRIKES ETC.. SHOULD HAVE ONLY ONE MINT MARK! THIS $7 STRIKE I THINK THEY ALL WHERE DOUBLE STAMPED! OR MOST OF THEM WHERE, SO ITS A VERY COMMON ERROR FOR THIS COIN! THE VALUE COMES IN IF THERE WHERE ONLY A FEW COINS MINTED THIS WAY,OR VERY FEW COINS MINTED AT ALL! IN CERTAIN YEARS THEY MINTED MORE COINS THAN OTHER YEARS! I HAVE A FEW RARE GOLD COINS THAT ARE DOUBLE STAMPED! ONE IS WORTH ALOT MORE THAN THE OTHER BECAUSE OF HOW MANY THAT WHERE MINTED THAT YEAR!! DOUBLE MINT MARKS ON ANY COIN IS A ERROR!

RICHARD