This is the first time I made a chocolat buttercream cake and I used the Perfect Crusting Chocolate Buttercream on CC. I stored it in the fridge after making it and it hardened up so I let it set out on the counter whipped it back to a soft consistancy. I then filled and frosted my cake yesterday and left it out on the counter in a cake carrier. Now a little more than 24hrs later it looks like its sweating grease and starting to melt off the cake. Parts of the cake is showing through. So my question is does this have to be refrigerated since A) it has tons of butter in it and B) its chocolate and a little humid here?

Where do you live? How hot is it there? How hot is it in your kitchen?
Exactly what buttercream recipe did you use and exactly how did you make it and exactly what brands did you use to make it? And what is the cake carrier you used? Brand new or used before? It coukd be a reaction from a new plastic carrier too.

I live in South FL and it has been humid I have the ac on low dont like it cold so it might be a little humid when the ac shuts down? The kitchen was a little warmer from the daily cooking. The carrier is not new. I never had this problem with my plain white crusting buttercream. So I thought maybe the high coco contents from the chocolate chips n high butter content might have something to do with it? I used the Perfect Crusting Chocolate Buttercream recipe here on this site. It had 2lbs of powderd sugar, 3cps of salted butter, 1/2 cp cocoa,melted Ghriadeli chips 60% cacao, vanilla extract, 3tlbs milk. For a smoother consistancy I used 2cps salted butter 1 cup crisco. I know I wont be using this recipe for a cake again.

It could be the weather then. This does sound like what i get on hot days here up north. I guess this is the reaction that frustrates the professionals so much. My guess is to keep the cake in the fridge and eat it quickly.