Can't create boundary surface between two closed curves?

Hi, this might be simple, but I’m just not seeing it.

What I want is to create a surface between two closed curves, two ellipses, one big, one small.

Somehow the Boundary surfaces component creates one big surface. I am able to do this with other closer planar curves, but in this specific instance it doesn’t want to work. I’m lost as to what the cause is, please see the enclosed file and the screenshot. There isn’t anything else to explain I think.

My goal is to create a surface in-between the two curves. (4.7 KB)

I have been able to do it with other curves, so I’m puzzled why the above example doesn’t work.
This is what I try to achieve as an example:

You can use loft or sweep 2.

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I don’t know why? Maybe the curves go opposite directions?

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Yes, I tried to use Loft first, but that gave a different error: (8.8 KB)

With Sweep2 I am lost as how to create the section, is there a quick trick to create a section?

What I’m trying to do eventually is make an intersection with other curves:

Maybe there are different (better) ways to achieve this? I was trying to go the route of using BREP | Curve intersection to solve this.

Thanks Joseph! This was the solution!

The curves do go in the same direction though. It remains a mystery to me.

With Loft Options it works!
Sweep2 need a rebuild curve !!!

And it works also with boundary surface. there is something with the curves, but what ?

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Ah you’re right, there is something with the curves. To be precise, the 7th curve;
Screenshot 2022-01-28 225651

I generate the curves by creating multiple polygons, and then raising the fillet to the point where they become circles. I do this because I want the option to also be able to turn them into a square, triangle, hexagon, etc. (8.5 KB)

Am I somehow doing something wrong?

Despite the invalid curve, the solution by Joseph still holds strong, which is another mystery to me.