If the card has a clear Mastercard symbol, if I may ask, what would be the reason for it not working?
As far as I know, the only reasons a card would not work is either the card issuer is not allowing cash withdrawals or the card brand is not supported (Mastercard definitely is), the old Visa Electron or Maestro in EU could be examples. I've seen cases where those are not accepted, for not being pure debit/credit cards.