Mirror needs to connect to cloud.estimote.com.
Demos don’t require access to Cloud. Mirror is designed to work offline, templates are stored on device and user data is provided by Bluetooth, so no WiFi is required.
Space “@” and “_” in network name should work (checked that).
Sometimes when Mirror is not able to connect, a reboot (unplug and plug again) can help.
It may take some time for Mirror to connect to network for the first time. Have tried to leave it turned on for few minutes and check if message have disappeared?
I suggest reading thread No connection to cloud error. There are some tips that may help to pinpoint the problem (check that WiFi scanner template).
To configure WiFi you need to connect to Mirror using Bluetooth. Since you configured WiFi this means that Bluetooth connectivity works (also screen says Discover Mirror… instead of Your Mirror is ready to use). It is strange that demos are not working. Could you elaborate more which demos don’t work and how? Can you check if they have the same problem on Android phone?
What do plan to use WiFi for?