I recently took the Wilton classes and tried the Wilton buttercream recipe with crisco (transfat free) and it won't crust! I even tried adding 1 TBSP meringue powder and it still wouldn't crust. When I used the cake dummy it crusted fine so my instructor thought maybe my cakes were too moist, but I like my cakes and certainly don't want them dry. Does anyone have any idea what I'm doing wrong? I'm willing to try a different recipe if it works better.

I'm thinking it's because of the transfat free. Not positive on that though.

What makes an icing crust is the amount of fat (crisco) to the amount of sugar used. Cut down a bit on the Crisco. The more fat, the less chance it will crust.
Meringue powder has little to NO effect on it at all.