Thickening problem "Surface which failed Check"

Hi everybody,

I have this imported (Rhino4) surface and I'm getting the error "Surface which failed check" when I try to thicken it.

I want to figure out why is this error appearing with such a simple surface (regardless of thicken direction or value), but I'm not finding conflictive geometry or something.

If I build exactly the same surface with SW then I can thicken it the same way with no problem.

I'm worried because, despite this time the surface body is very simple and I can remodel it, I don't understand why I'm getting the error with the imported one and the time will come that I will need to do the same with more complex surface bodies and less time so remodel won't be an option and I will be in real trouble.

Any idea about why is that happening or how to avoid the error??

Thank you so much!!

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