(Portland, OR)  --  Multnomah County residents are being warned of a phone scam in which the caller claims to be with the sheriff's office.  Deputies say the caller demands payment for an outstanding arrest warrant and tells the intended victim to purchase a Green Dot, MoneyPak, or Vanilla Network reloadable card to make the payment.  Authorities say none of those who reported the scam lost any money.  The Multnomah County Sheriff's Office says it would never call anyone to ask for a payment over the phone for warrants or traffic fines.