This happened to a bunch of us here (dis forums) who wanted Dessert Party ressies for Sept of 2014. Our window opened and we couldn't do anything! Not by calling. Not online. To further frustrate us, no one had any answers as to why we
couldn't buy tix. Only after many calls, emails and daily sharing info on a thread here, we finally were told that WDW was waiting until the
MNSSHP dates were finalized. Mind you, the party dates had already been released but I think Disney was watching to see how these filled up and if they could profit by opening up additional party dates, they would. So they couldn't sell tix to the Dessert parties IF there was a possibility that they might want that date for an additional MNSSHP.
It took about 6wks AFTER our 180 day mark til we could finally buy the Dessert Party tix.