Well, I am in the midst of making a princess castle cake for my daughter's 6th birthday party...tomorrow.  I baked the cakes yesterday, put them in the fridge, made the icing yesterday as well. During construction of the castle base, i had to piece together part of  of the base.  For some reason, an entire portion of the cake fell over.   It was only two layers high and just being crumb coated with icing.  Arrgghhh!!!!!..  Needless to day, I was upset and expected to have to spend the entire night baking and decorating.  After a short break, I decided I could use the remaining cake and modify the design.  Part of the problem may be the humidity here which is a bit higher than normal. I also noticed the icing starting to melt a bit.  The cake is currently in the fridge...I am praying it doesn't fall over in there while it is chilling. 

Are you saying that your cake was 4in high and part fell over?  Do you have a pic?