I know what you are talking about, I have the same problem. I recently made a box cake and it was 3 layers. I covered it with fondant, it looked perfect. When I covered it the cake was still semi frozen. Then the cake started to sweat from the condensation. That is when the fondant started to wrinkle and the cake started to shrink! I lost 2 inches off this cake. If the cake shrinks your fondant will wrinkle.
This is where I think I went wrong:
a. the cake was not at room temp when I covered it
b. I used a box cake mix that was not firm enough to withstand the weight of the fondant.
I hope this helps, I do cakes for a hobby I am semi talented,LOL.
I am going to do another experiment to see if my theory is correct.
Tanya 
also, if you used satin ice.. that can wrinkle like elephant skin too. i know from experience. yes i kneaded. it good ..use shortening on my hands,etc.. but satin ice will wrinkle fast.. all the other comments that you have received is also true..hth
I use DH box mixes under fondant all of the time and have never had this happen to me. I never freeze cakes because I don't like the taste/texture of thawed cakes (matter of personal preference only), so I can't speak to the frozen/thawed issue that you mentioned.
I did use Satin Ice and my cake wasn't cold or frozen. It wasn't like the pictures (adorable cake btw wrinkles or no wrinkles!) but more like tiny cracks like dried skin. I tried to use some shortening on my hands to smooth but it didn't work too well.
Fondant will have smallish cracks if it dries out too much while you are applying it to your cake. If it is too dry or too cold, it will "crack" as stretch it to smooth it out on your cake. If this happens, the only option is to try to cover it with decorations or take it off and start over. HTH!
What a shame this happend to you, your cake was really lovley before the icing sank! I can honestly say, ive never seen that happen before , and ive only ever worked with fondant! wish i had some advice though, but i dont. Just wanted to tell you your cake was lovely 
OH, and that i use betty crocker devils food cake mix all the time, infact for almost all my cakes, and never had a problem with it being unsturdy enough x
I don't think covering a cold cake makes the cake shrink cos I've done that a number of times when in a hurry 
, the worst that happens is that the fondant gets sticky but will dry up later. I think the shrinkage was as a result of the cake mixture you used,some mixes are not meant to be covered with fondant cos they are too light and cannot support the weight of fondant like some sponges and angel food cakes.
I did use and my cake wasn't cold or frozen. It wasn't like the pictures (adorable cake btw wrinkles or no wrinkles!) but more like tiny cracks like dried skin. I tried to use some shortening on my hands to smooth but it didn't work too well.
Satin Ice will tend to do that. 
It's one of the reasons I don't like Satin Ice. However, if you roll on a silicone mat, it does help. I find also that if I kneaded it til almost warm to the touch before I applied it, it worked better.
Tanya, your cake was adorable. I think it succumbed to a bad case of settling. Covering a cold/chilled cake is actually just fine to do. Covering a frozen cake is asking for all kinds of trouble. The best rule of thumb is to crumbcoat and allow to settle for a minimum of three hours to overnight at room temp. Then you can chill it for about 20 minutes before applying the fondant. A frozen cake still has a lot of chemistry it must work through before it is done settling. Sorry that happened to such a cute piece of work.
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