Cannot find page after changing settings to use year-month-name system

I cannot find a post or a page after changing settings to use year-month-name system. There was only one post in the system as a default install and when I changed the naming convention to use year-month-name, I edited the existing post and saved it.

Now I cannot access that post from public indexes, nor can I access pages. The home page displays the article and its link appears in the side menu, but clicking them gives a 404.

They edit ok like /2011/05/welcome-again but won’t display. I checked the permissions on the folders and they are write,write,write.

Do other users get into trouble when they change this setting?