Hi alexito - Network needs the input curves to have a kind of grid arrangement similar to "latitude" and "longitude" lines on a world globe.

In your example there you've got one curve like this:



That one is fine, it is like a line of longitude on a world globe, running from the "north pole" to the "south pole".

But then one of your other curves is a long closed loop:



This one is the problem one - it is one big closed curve and does not have end points that match up to the other longitude line (the one I showed in the first image above).

So to fix this, you need to cut that long curve into 2 pieces, then you can use Network on them.

Here I show the pieces slightly separated for illustration:




You can cut the long curve by selecting it, then run Edit/Trim, select that other curve that touches it as the cutting object and click Done (or right-click in a viewport, that is a shortcut for "done"), then click Done again at the prompt that asks you which pieces to remove, since you want to keep all the pieces.

Once you do that you can then select all those pieces and run Network on it, but you also have a kind of sharp corner in that longer curve as well which will produce a sharp corner in the Network generated from it, you may want to turn on control points for that curve and delete that sharp corner if you don't want that.

- Michael