I changed the permalink structure according to PC's

I changed the permalink structure according to PC’s directions here https://premium.wpmudev.org/forums/topic/how-to-change-network-default-permalinks#post-440253, now the new structure shows in the browser bar correct, however, I get “page not found” in the top tab next to the favicon and in the title. http://wpinstasites.com/test-new-permalink-structure/. Can this not be done on an existing multisite or only on a new multisite install before adding test sites and development?

I posted on that thread as well. Should I have created a new post or ask for assistance there? Just trying to understand correct protocol.

Thanks for your help – Jan