Hi Brandroid, if you look very closely at your middle curve, it's subtle but it's a little darker than the others:




Then if you select it and look at the object type indicator, it says it's a "Closed crv":




So that means that curve is doubling back over top of itself, that's why the Network won't work with it, all the curves for one direction in a network should be either all open or all closed.

That middle curve will need to be fixed up to not be self overlapping for Network to have a chance. I'm not sure that you're going to get a good result any though because you've got a very tight bend just in one spot there, I guess it looks like you're hoping these spots will match up with each other:




But what's probably more likely to happen is spots like these will be actually matching with each other, since those tightly bent areas are at fairly different distances along each curve:




It generally isn't good to have such tight bends in a single network, it would probably be more controllable to build that in separate pieces, with one piece matching to each broad slightly curved sheet and having tight bends formed by fillets or blends between those pieces.

Hope that helps.

- Michael