Edit popup hangs and hangs

I created a new popup and edited it several times without incident. However, then it started hanging on the edit screen and never never loads for me to be able to edit. I logged out of WP, quit my browser and relaunched, even tried a different browser, same thing! (Both Firefox and Chrome). I need to add one last edit but can’t do it.

The page I need help with: [log in to see the link]