Well, most casinos have this rule, however in your case they should have contacted you when they had the change , atleast in my opinion.
I thin you should follos K´s advice and try and contact them again and ask them to change your account to dollaars and have the winnings transfered.
There is just so many things to look out for in online casinos these days =(
They should have done a sweep of all EXISTING accounts when the rule was implemented, and any accounts found to have the wrong currency should have been locked. This would have ensured that players returning to an existing account could NOT simply have "walked into the trap". They would have had to ask CS to unlock the account, at which point the currency issue could have been sorted out by switching the account to an acceptable currency before unlocking it for the player.
By allowing the account to remain active, the casino broke it's OWN terms by allowing the player to redeem a free chip.
RETROSPECTIVE changes like this should ALWAYS be notified because there is NOTHING the PLAYER can do about this, they have ALREADY been allocated the currency, and CANNOT simply comply with the new terms, but have to have the account closed, and another opened in a new currency.
It is a little different with the usual types of changes, which players can read & comply with on their EXISTING account.
This has now left many "traps" for players who registered under the old rules, and have no power to comply with this new rule without closing these existing accounts.
Rival really should have thought about this right from the start, and implemented a currency policy before they started accepting players. When Rival came on the scene, this was already common policy among online casinos.
I can't see why this can't be dealt with during the registration process. When the player selects their country, ONLY those currencies permitted for their country should be selectable. This would ensure NO players end up using the wrong currency.
Casinos DO make use of location details, and IP geolocation, to control many aspects of the experience. It seems that they would rather leave traps in place for the unwary, rather than do what they can from their end to ASSIST players to fill in their registration correctly.
This is 2011 - I am not buying into "can't be done" with the current levels of sophistication seen in software and hardware.