Trouble with Loft

I try to loft 2 surfaces (one is from Patch, other is from Curve Network) with grasshopper. This is doesn’t work, and return no error. I think the problem is my upper surface, but I can’t fix it!
Here is the files, if someone can explain me :slight_smile:
Loft problem.3dm (3.0 MB)
Loft (1.9 KB)

you must look at your inputs.
For loft curve must be on a list. Here there are on two branches of a tree. Each one has just one curve. So you are asking make a loft with one curve. There must be some warning for that, but it outputs “null” instead !
So flatten inputs and add option of loft

Thanks a lot for theses informations…! It works better :slight_smile:
I have to learn more about theses options: Flatten, Graft, Simplify, Reverse, Principal… it’s vague for me.