I had this problem and thought it would be nice to post a solution.
It turns out that MIONet doesn't work when HTTPS is enabled (instead of HTTP) .
To solve the problem, all you have to do is to use HTTP rather than HTTPS.
Login to your WD World Edition device (through https probably).
Enter "Advanced Mode" by clicking the link at the top right corner of the screen.
Click the "General Setup" button.
On "Web Access Protocol" choose the "HTTP" option (not HTTPS).
Now go to the Remote Access screen and try to register your device with MIONet again.
Hope that helps...