You could try sealing it in an airtight container for a while and see if that helps. Is the frosting hard all the way through or did it just crust?
What type of icing is it? (Sounds like it could be fudge...)
The following thread has links to popular CC recipes for crusting American b/c's, fondant and doctored cake mix (WASC in various flavors):
http://cakecentral.com/cake-decorating-ftopict-605188-.html
Here's a link that describes the different types of frostings/icings:
(And has handy troubleshooting chart on last page.)
http://tinyurl.com/yh44gu
HTH
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