No, it has nothing to do with fees. The input to the transaction was taken from previous unconfirmed transactions. The network couldn't verify the input as existing as it is unconfirmed so the transaction was rejected. The casino will have to update their routines to handle building transactions correctly.
That's great information. Do you know if something like that could happen if someone sent Bitcoins from the standard Bitcoin client with -paytxfee=0 ?
I'm pretty sure the standard client will not let you send a transaction from unconfirmed inputs. But then again I have not tried.