Please don't create pages and categories with the same URLs.

If you're using the Web Directory package or Publishing package or Yellow Pages package, please don't create pages that have the same URLs as categories and don't create categories that have the same URLs as pages.

Example: I have page with URL: http://www.yourdomain.com/environment/ so if I create category that will have the same URL, system will not be able to differ where page and where category.

That's it!