rolled buttercream sliding off of a cake

  Could someone please tell me why the rolled buttercream slid off of a cake. I used the recipe of 1 cup crisco, 1c corn syrup, vanilla, salt, lemon oil and orange oil and powdered sugar. 7 cups of it.

I put it on the cake and the side of the first layer slid down to the bottom of the cake and pulled some of the cake off.  Also it got oily. I got this recipe from yummy arts and I followed the recipe as given.  This buttercream had a real good taste and the texture was not like fondant so I liked that about it.

why did it slide off the cake , yes I did put buttercream icing under it.  Why did it get so oily?