I'm having the same issue with the "size" item specific field not being present and trying to add it does not work. This seems to be an issue with any of the women's clothing items but not the men's clothing. Thought about creating the listing as a Men's clothing item, posting it, and then immediately revising it through eBay, but that's just doubling the effort to get something listed. Filed a help request through Auctiva but typically this takes several days until they get back to you. Very frustrating.