Extruding closed curves doesn't work properly!

velizar.3dm (457.7 KB)
When trying to extrude these closed planar curves, it creates an open polysurface but detects it as a closed extrusion. When I try to use the “Cap” option it says that the object is already closed.
How can I quickly fix this?

dear @maimun2002 there is some self-intersection in the lower loop of the “z” - the inner curve…
i ll upload a fix in a few minutes…

the first screenshot show s the self-intersection.
it s a pity, that the
_intersectSelf command does not find it - maybe because of some tolerance-issues.
and also, the single curves all extrude well…
i found it by stepwise try & error

to fix it - easy:
turn on control points
move the controlpoint that causes the self intersection

after fixing the curves - extrudeCrv works like expected.

velizar_fixed_rh6.3dm (348.5 KB)

kind regards - tom