solid non manifold

[TECNOMODEL]

I'm trying to create a 2-curve loft, a circle and another shaped loft.
the message "Input sections have created a solid non manifold"

What do you mean? and above all, how do I solve this?

Thank you.

 

[ninfh]

basically inventor is saying he can't or doesn't know how to close the loft, you could try to make a loft of surfaces, close the ends and then pass it solid