Hi Tom, I took a look at your file but there's 31 curves in it so I'm not sure where I should be looking for the question you had here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=8468.9

Could you please simplify it and only have the curves in it that you had in your screenshot with the green arrows?

Certainly it is going to be difficult to manage so many curves all needing to intersect each other with everything swooping around in 3D at the same time. It might be better to use a smaller number of curves if possible like only focus on ones in one direction and loft between those or something like that.

- Michael