Try starting it from scratch, what I found is that as I started a new listing, my old 'lost' one came back. Weird but true. So it is saved, but its not obvious how to retrieve it back. Basically it's a bug which TradeMe have placed a very low priority on getting fixed.

30 minutes or so ago I clicked SAVE LISTING and received a message in green that my listing was saved and I cold continue with it later. When I click the "List a New Item" I don't get the "Continue or Start Again?" dialog. Come on Trade Me!, how the heck can such a large company ignore a BUG in their code for over 1 year? One developer could solve this easily in no time at all.