Custom error page: The path is either invalid or you do not have access to it I'm trying to add a custom page, by using admin/config/system/site-information

When I enter the field, as follows:

Default 404 (not found) page

http://mysite.com/errors/404.html


It shows the following error:

The path 'errors/404.html' is either invalid or you do not have access to it.

Though when I enter in my browser: http://mysite.com/errors/404.html it opens just fine.

So, what's wrong with Drupal, why it doesn't see it?
When you go to admin/config/system/site-information to enter the path in the field Default 404 (not found) page, you don't have to add .html just write errors/404 and it will work.