Dear slotplayer,
Some of our forum members have been saying about this too.
It seems if your detected IP address is USA (or possibly certain parts of it), then this happens (I’m assuming intended to deflect players that can no longer create new accounts).
However, (Rewards – and any other MGS casinos), if you’re still allowing USA players with existing accounts to play – they would need to re-download and re-install.
One possible ‘way around’ is to just pop the install file on your own server (if that’s allowed of course), but not sure how the installer works so I’m waiting to hear back from forum members with existing accounts if this works (just trying one casino [GoldenTiger] for now – and will of course delete the .exe file from my server if this is ‘against the rules’)..
Hopefully Yaniv/Rene can let us know the full / correct answer and hope this helps 
Cheers,
Geno