Did you stick it in the fridge and condensation is doing that?
Did you use ganache as filling? Was it to warm when you did it? What ratio did you use for the ganache? I'm trying to understand why you said the ganache won't hold up to the cake. For filling and frosting I use 1.5:1 choc to cream. I le it set up in the fridge and then put it on the counter an hour before I need it to bring it back to room temp.
I agree if you refrigerated the cake, as it comes back to temp it could cause this issue.