I like to decorate with butter cream icing but if the board I put it on flexes at all the frosting cracks.
1 pound of powdered sugar
1/2 c. crisco
flavoring
and water
what am I doing wrong 
Welcome to cake central. Shortening based icing tends to crust. It makes smoothing the icing easier, but flexing the board will cause cracks.
use double boards, plastic bases, or cake drums (thicker bases) or even masonite or thin plywood. No flexing, means no cracks.
You can also try one of the other buttercreams in the recipe section.
I've read on a previous forum that a drop of vinegar added to the butter cream icing will make it not crack, it doesn't change the taste because it is a small amount, but will prevent the cracking. I've tried it once and the icing didn't crack so there might be something to it.
The more your icing crusts, the more tendency it will have to crack when you move it around. (Especially if you dont have it on a sturdy enough base) Anyhow, your recipe has quite an awful lot of sugar to fat. Meaning it must crust quite a lot. Maybe try 1 cup fat to 4 cups of sugar and see if that helps a bit. It will still crust fine.
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