Did you buy an OEM or COMPATIBLE ribbon? If you bought a compatible, please make sure you have bought the correct design for your typewriter. Some compatible ribbons come with a lug that prevents them from sitting correctly.

I note that you posted this problem over a month ago. If you haven't solved the problem by now, i would advise you to contact www.inkribbonpaper.co.uk. I have used them a number of times with great success for our smith corona, brother and royal typewriters