Quote from Rocko Bonaparte:
I've seen neural networks used for classification by encoding the outputs to represent different situations. Say, detecting letters in an image would be a classification problem, and the neural network could have a different output neuron for each letter.
The "regression" method as in the Wikipedia article is something I tried to do once by clobbering together some random indicators with their first and second level derivatives (derivatives in the differential equations sense, not in the financial sense). It didn't work, and I'm pretty sure it was because the indicators weren't good to begin with. None of them were profitable alone, nor did I ever find a combination that helped. The neural network was a red herring that side tracked me for months due to a few bugs in its implementation; it was fools gold in the end.
I could see a neural network basically curve fitting problematically if it's applied to a narrow set of data without having enough data to counter it. And that's where curve fitting would be a problem with anything else.
Your experience is common. Successful usage in this very complex area often requires an MS in Computer Science. Kicking around a few data files seldom does it.
To your point on data: A large training set is required along with smaller sets for test and validation. For hourly EUR/USD about 24,000 bars work very well for a trade window of up to 12 hours into the future.