Your ruled surfaces are not always planar.
Check this:
Region Differentce problem V22.gh (68.0 KB)
Wow,Thanks Martin.
You are really very patient and solicitous. Your solution is really creatively and very very inspiring.Your solution really fit my need.Thanks very much.
By the way, following this tip from you,I found the Project Along component, and found an other way to solve my problem.
Thanks again.