Paper Jam error 3110cn(077-901).

Hi all hope someone can advise?

i have a Dell 3110cn colour printer which has a duplex fitted.

when trying to print a double sided document it prints the first one side of the sheet but the second sheet causes a paper jam. On opening the main front of the printer the second sheet is resting against the (sorry for the description, the black film).

i remove the jam and it then does the same thing again?

any advice would be most appreciated