Try this it may help,
start the Yeti Vision game and then hit (alt + tab) to get back to the main desktop screen. You may find a message from your firewall asking you if you want to grant access to the Yeti executable program, say yes to it and you should be ok.
Every time an executable program on your computer is changed you need to grant it access all over again and this may be the cause of your trouble.
Good luck
DaffyPluto