Friend Book troubles

i got friend book and it worked last night, but today it refuses to work. i am testing on the same two iphones. what happens is, when i shake them, they get through the 2nd stage, but when they reach the third, it fails. then on my iphone, it shows a different picture on the 4th stage and says dont do this to your iphone. how do i get it to work again? i am in the US btw.