A surface that won't split

I have two surfaces that I can’t get to split. I seem to be able to use the surface to split another but can’t split the one I need. I’m trying to split the red surface. Hope someone can help. Cheers Split problem.3dm (558.7 KB)

Hi Greg - the black object has overlapping faces - if you check for naked edges you’ll see what has to be fixed.



Thanks, on closer inspection the curves used to loft were a bit confused. Sorted now.