Have you read this thread?
http://www.cakecentral.com/cake-decorating-ftopict-1353.html
Maybe there is something in there. Sorry I couldn't help more. I have had trouble with that as well. All I did was make sure my cake board was more stable. It seemed to help the next time.
I agree, it's a more stable board that you need. I use three cardboards and sometimes it still cracks a little. I've now gotten so that I put the cake onto the three boards and frost it. Then, before it crusts, I slide it onto a solid wooden board. I leave it on the board until I'm finished decorating it and then slide it carefully into the box. Once in the box, it is a little more stable. If I know I'll get it back, I'll just send the board under the cake box also and tell them to slide the cake out. I only do this with folks I know pretty well; otherwise it might seem strange. 
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