After changing Wordpress Permalink to "Post Name" then Page not found

[admin]

I have wordpress site, after i changed the permalink to "Post name", then the sub pages (but home page is working fine) are not found "<strong>Error occurred: 404 - not found</strong>" . But if i changed to page ID - Plain url, then it is working but it show page ID in the url.

Pls check my screen shot of wordpress permalink <a href="http://prnt.sc/dfgba3" rel="nofollow noreferrer">http://prnt.sc/dfgba3</a>

thanks