This signup and verification for continuing the game is the worst registration process *ever*. I would swallow entering the credentials in three different places, but this piece of shit Counterwallet is broken, signing the message gives different signature every time?!? No wonder Let's Talk Bitcoin site says every signature is invalid. Has anyone ever tried this wallet before torturing us to use it? Or is it broken intentionally to force us to make a donation so we could continue the game? Really wouldn't bother me to donate for continuing the game but please, please, don't make us go through this wallet.
Last ARG forced us to have payware MineSweeper game to play and that made very few people to abandon the game, but Counterwallet may decimate players this time, at least I'm out if I have to use it.
I have tried using the brainwallet to sign the message but I am also getting invalids, so maybe the problem is not with the counterparty and it is on LTC site.
It very likely is at least a Counterparty issue, try pressing the sign button several times without changing the message, every time it is a different signature.