how to loft and sweep two lines

Dear all

I'm just a beginer and I don't know much about Grasshopper. And now I'm in trouble with Loft or sweep in grasshopper.

I woul like to make new surfaces between two shell shaped sufaces. In order to do so,  first I offset surface, second I made planes. and I had planes penetrate two surfaces(original and offset) and made intersection curves. 

And Now I try to loft two groupes(BBX, in this case) of lines but it doesn't work. Loft refuses connecting from BBXs. Of course, I used Fratten and Graft to make lines on the same branch.

But I don't know why. Sweep also doesn't work. Steps I did are wrong ?

 So please someone tell me how to use Loft.

Thank You so much.