OOTB Znode has the SEO Friendly URL field allowing trailing slash turned off by default, which is why you are seeing the error. You can configure the following web.config setting in both the webstore and admin to allow this SEO requirement.

If you want to set a custom URL that has multiple trailing slashes, such as the following, /cordless-woodworking/custompage

You can configure the following web.config setting in both the webstore and admin to allow this SEO requirement.

• Set the flag runAllManagedModules to true in both the Admin and Webstore > web.config files to allow "/" in the SEO URL.
• Recycle the app pools if you are planning to do this on a hosted website.