In the past I've made several cupcake bouquets with no problem...but this weekend....the icing kept sliding off the bottom row...the icing roses slid off completely intact.  At first I thought it was because I used a cream cheese icing which may have been too soft, then I started with new cupcakes and a traditional buttercream icing with shortening, butter, vanilla and powdered sugar.  Icing was a stiff consistent beautiful for the rose design but kept sliding off. Help - I did nothing different than all the other times!

The cupcakes were cooled right? 

yes cooled and refrigerated thanks

If you have only made "several", you may not have made enough to have arrived at a consistent, successful method of construction.  It may not be the recipe at all.  You may have gotten "lucky" with the first two, and now problems are showing up.   There are far too many variables for anyone here to provide a meaningful answer.

Your best option is to do a search on this site (if the new format will let you...), and on google for cupcake bouquets.  Study the different methods and then do at least 3-5 to see if they all turn out well.

Good luck!

Same thing happens to me. I usually do the Wilton's buttercream recipe. I've noticed that once the buttercream crusts they start sliding off. I've tried the angles of the cupcakes and they still slide off. I was thinking of using a buttercream that doesn't crust but that the consistency is good enough to hold the roses' shape. 

If you found a way to stop this from happening, please let me know :)