interpolation even degrees error

Hi everyone,i want to interpolate a few curves and then create a surface using the network surface component.The first problem is that i am having an error(orange balloon) at the curve inerpolation component saying "Interpolation does not allow even degrees". My second problem is that when i connect the U and V curves,which i interpolated as 3rd degree curves,with the network surface component the result is null(no surface),even though the component does not turn into red or orange colour. I don't know if the second error is due to the first one and i would like to hear any opinions on these two problems.Thanks