I have the same issue when I installed the plugin.
Old pages (before plugin installed) were not accessible anymore. Every action (updating menu / adding pages-media-post) triggers the error as mentioned above and a 404-error when accessing them.
Even deactivating the plugin keeps causing trouble. Going to reinstall everything – is going to be quicker & easier then waiting for a (possible) fix.
Plugin looked promising but causing too much trouble, as I see other WP-site owners experiencing the same problem. Seems the last version is a Beta-version.
