I covered a cake with buttercream tonight...the same I've used many times before and it's always crusted...but it's not crusting. Could it be because I used it from the freezer? (thawed of coarse )
I've used mine from the freezer a lot and never had that problem... Maybe it did but I don't think that would be it... here's a bump!
My guess is something to do with the humidity where you are?? Sorry I can't be more of a help.