Question: The URL <http://www.routerlogin.net/> isn't working on an internal network when I try to access it via a wireless connection. Why is that? What is the best way to configure this router to be able to access the router via a wireless connection to manage it.

Answer: 
I found the solutions, there is an option called: "Enable Wireless Isolation", it was checked, hindering the router via wireless.
I got this error because I do not use my N300 as the primary DNS. If you temporarily change your networks settings to use the AP as your nameserver, then it is possible to connect.