I've also had that problem when creating some of the demo content. It is not a problem with the theme or framework; it's a combination of an issue with how WP manages its menu system, and a limitation created by your server settings.
This WP support thread explains some of the possible causes.
This plugin can tell you exactly what you need to do to fix the issue, and warn you when you're close to reaching the limit.
I had to contact my server provider to have them make the change to the PHP settings on my dev server, so you may also have to do the same, but hopefully that plugin will be able to tell you a way to do it on your own.
I hope that helps.