Ah, we just still aren't talking about the same thing
Just below the "Create a similar listing" section is a link that says "Saved Listings". Click that.
From that page, find the ad that won't load for you, and check the box next to it (don't click on its title though, that will go to the page with an error). Above the box of saved listings are buttons. Either hit "Post Now" or "Schedule", if you don't want it to go up to eBay immediately. Either of those may work for you.
If none of this works, we'll have a fix figured out by tomorrow.