The message is somewhat misleading. It is correct only up to "The Spline method could not be used" and in fact the implementation does not currently support derivatives. In such cases, Interpolation falls back on the default method (Hermite) which is why sf2 and hf1 are the same.
Your x values are more deeply nested than the ys6 and the dys6. Could that be the reason?
{{{1}, 0.130962, 0.}, {{2}, -0.376878, 0.387584}, ...
Don't think so. That's the way the documentation says to do it, and it doesn't work at all if I don't do it that way. Try it yourself!
