EX6100 New Router

You need to be connected to the Wi-Fi signal broadcast by the extender in order to www.mywifiext.net to work.

If you still have trouble, then perform a factory reset of the extender. According to the manual, you'll need a paperclip. Press the button inside the little hole until the Power LED blinks amber, then release the button.  Wait for the Power LED to turn solid green.  Then proceed to set up the extender as if new out of the box.