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: 
The router may not support wireless logins by default. Most routers require the feature be enabled via wired connection before accepting wireless access.
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.