_find0 Function
This is a function that Netica uses internally to find the state of a discrete node having numeric values associated with its states, given one of those numeric values. If Netica gives you a message saying there was an error evaluating _find0 (z, x0, x1, ... xn), where the z and xi are numbers, then your equation is supplying illegal values, even if you never explicitly used _find0 in your equation.
The value of z must equal one of the xi, or else the equation is saying that the node has a value that is not represented by any of its states. You can change the equation to only supply numbers that match those attached to the state of the node (perhaps using nearest), or you can change the numbers attached to the states. Or, if you wish it to be able to match numbers in between the xi, then you should change the node to a continuous one, and leave the same set of attached numeric values as its discretization thresholds.