Help booleandifference and making a solid from 2 curved surfaces

Hello there,
When I try to do a boolean difference it gives me an error and creates a new group in one of the edges of the surfaces I want to subtract. These surfaces were created with sweep1.
I also need to do a solid object between 2 curved surfaces.

there is no general answer possible with your description the image shows nothing that could allow even a guess and does not reflect the title in the least,
i wonder what is going on recently with all these obfuscated posts here recently…

why not post your geometry?