Two things that I know of can cause the crusted icing to crack. The first is waiting too long to smooth the icing. If it is too crusted, it will crack. The other is having too little support under the cake, so the cake flexes a bit when the cake is moved, which makes the crusted icing crack. I don't know why they make the cake boards so thin, especially for the larger sizes. You have to double or even triple them to prevent the flexing. (Or use something thicker like foamcore or masonite)
I had this happen to one of my cakes. Indydebi suggested I add a bit more milk to my frosting and I haven't had the problem since. You might want to give that a try, just to make sure your frosting isn't too dry to start with.
My first suggestion: Use Indydebi's Buttercream Icing. Here's the link:
I would also agree with redpanda: Don't wait to long to smooth, and make sure your cake has a strong base.
HTH. Good luck.
It looks like you used only 1 cake board. Even with 8" round layered cake, 1 board is not enough support. I always use 2 with this size. That should help your class BC from cracking.
Another little thing I do with cardboard cake boards is to put two or three together, but make sure the corrugated lines are not all running the same way. This seems to make it a little stronger.
Good job on your first cake! Search around here for different butter cream recipes. Make sure you follow and measure ingredients exactly. I've had to make many batches of buttercream before I found one that worked for me, same goes for baking.
Along w/the already suggested thing to do, I suggest you thin the icing just a bit more. It should be thin consistency when using the Wilton Class B'cream recipe.
Ok so double the borads and make sure that the icing is thin, got it. Another question, how much icing do I put on the cake? Alot or a little?