Once the holy grail of travel hacking, error fares are the occasional 'fat finger' mistakes that occur in spreadsheets with airline fares. These spreadsheets (or would they use APIs these days?) still feed online travel agencies with the multitude of different fares and fare rules that airlines use to optimise yield.
So every now and then, you can fly business at economy prices, because someone forgot fuel surcharges or left out a zero in a base fare. And then these fares are published on forums and websites such as www.secretflying.com. And then people start booking them, thinking they will outsmart 'the system'.
Boy, have I got news for you. Airlines follows these forums too! And they correct their mistakes. While some airlines sometimes still honour error fares, I wouldn't count on it. I tried it once, with an error fare of some 780 euro Florence - Bangkok - Dusseldorf (in essence it was a single ticket within Europe with an amazing opportunity to make some detour to south-east Asia).
The error was acknowledged, the booking was partially canceled, and I had to get on the phone to see if I could get my money back. Luckily that happened, at least a month later. Also I was so lucky to get a full refund, also for my booking costs at the online travel agency that I had used.
Now, compare this to the legitimate rates: I can get tickets from Europe to Bangkok for around 1,200 EUR, with an occasional drop to 1,000 EUR. Thus it's a simple question: why bother? With error fares, you need to postpone your travel arrangements, because of the risk of cancellation. And would it work, I'd be scared that I would be denied boarding.