The matchsettings (also called gamesettings or playlist file) file you specified in the command line is wrong.
If you save your game settings in
UserData/Maps/MatchSettings/royal.txt, your command line should contain
You can also check for the file permission if you are using Linux.
Your MatchSettings file is specifying an unknown mode, change it to the value
<playlist> <gameinfos> <game_mode>0</game_mode> ...
Happens on servers which are online for more then 30 days. Restart your server to remove this message for players.