The greyed out "Scan Now" button is most likely due to the recent change in WiFi Guard. In the latest version, WiFi Guard switched to displaying more user-friendly network adapter names, to help users identify their network adapters with greater ease. However, the small temporary inconvenience for the existing users could be that the program may no longer recognise their previously selected adapter.
The solution for this is very simple. Please open WiFi Guard settings and reselect your WiFi adapter from the list. After that, the "Scan now" option should become available again. You will need to do it only once. After that, everything should work fine, as it did before.