Can't move past "select categories" on new listing. A message keeps telling me to select a category every time, even though I do!

[cushions1]

I've successfully posted 4 new items, and am now stuck on the 5th, which is not much different from the other 4. To create the new listing, you have to enter keywords, and a category, which I do, and then I get a message saying I have to select a category. Over and over this happens, and so I can't move on.