I'm not very familer with CPS, My guess would be that there is some double edges where the truble starts, giving you that problem of multy shell's inside.

I normaly work in poly only eather with a proxy, or subD proxy. Don't know if you can do this but tern on the heads up display for poly information. Seclect sevral verts or edges around where it starts and if it list more than you think you selected thin you know you need to get rid of them. Maybe you could try to run the poly clean up on it.

Sorry thought probably would be more help if I used CPS.