Something must be going on with their site in general. I've been trying to list new items and it keeps getting hung up. I listed 3 just fine, and now I keep getting stuck. Hopefully they resolve it soon.
I just got one to work! Try reloading the page and proceed, mine glitched during the processing and froze for about a minute, but it did go through and I was able to print it. I'm hoping this means they're working on it.