We've fixed several things with our Zenfolio uploader in response to changes they've made to their API over the years, so an old thread may indicate that a problem was fixed, but that doesn't mean that some other change on their end won't necessitate a change on ours.
We've set up new Zenfolio trial accounts and encountering the same errors. Our older Zenfolio test account, which has existed for several years, still connects just fine, so there is something about these new accounts that doesn't play nice with how we are using their API. We have gotten in touch with Zenfolio and are awaiting a reply. It may be something they need to fix on their end. In the meantime, since you just set up the account, if you are open to alternatives, I'm not aware of any issues with the other image hosting services we provide uploads for (Photoshelter, Smugmug, etc.)