I've been using ATMs in Greece for a few years now (ever since they became available). I've never been had any trouble before until 2 or 3 weeks ago. I was touring the Cyclades (I know that's not Plakias!) but I visited a few ATMs on Naxos and they all went right through the process then said something like "Sorry we are temporarily unable to process your transaction - please try again later". I had to get some cash quickly as I was going to some small islands where I knew there were no banks (and therefore you can't use credit cards anywhere). I went into a bank and went through a right rigmarole (passport, phone call, various forms, €5 charge..) but I got some cash in the end. About a week later when I got back to civilization (Mykonos), one evening I tried to use an ATM and started getting the same message again - what was going wrong I thought. However, the morning after, the first ATM I tried worked first time.
Greecemad