The answer is there in plain text:
Since the system was turned off or lost power during a Wi-Fi Competition or a Random Matchup, you cannot participate in a competition or a Random Matchup for one hour.
your game has been barred. I don't know what you can do except restart or try and change some game ID variables in the pokesav (but I'm no expert).
Try refreshing your Internet settings on your DS by removing our DNS for example and see if that helps. Otherwise you may have to start a new game. Nintendo have gotten very annoying with their new 3DS rules!