Good morning I am new in cake decorating but a few weeks ago I made some cupcakes for a parent school meeting and I use the Wilton recipe for butter cream  which is the only one I know how to do... But after I finish decorating the cupcakes and place them in the refrigerator the next day the butter cream was like a little hard and not so good. Is there a way to fix that?? or do I have to put a big box in my refrigerator to keep the cold out of it????

If you are making the Wilton recipe is it with butter or shortening? 

Either one will get hard in the fridge however, when it comes back to room temp it should not change in taste.  If you make the recipe and use either water or milk the ratio of confectioners sugar to the milk will allow it to stay out of the fridge.  If I want a really rich icing then I use heavy cream otherwise all my cakes etc. stay on the counter til delivery. Another thing, when you make the icing be sure everything is mixed together well and then I just let mine mix on med until it is light and fluffy. No need to mix on high as your icing will have air bubbles, which you don't want.

Great info by @cakegrandma, but I'll add that icing placed in a "regular" fridge with other regular foods can have a tendency to pick up those flavors.  So if the icing had a funky flavor, it may have had more to do with with the evening's leftovers and not the recipe used.