Friendly URL

Hello,

I deleted the friendly URL under the Meta Data Tab for a certain sub-page and since then, the website comes up with Error 500: Internal Server Error. I went back to put the URL back but the option does not appear at all on the meta data page. 

Is it the deleted URL that may be causing the error on the site? I am very new at this and can not think of anything else that may have caused it or ways to solve this issue.

Kindly help.