Connectsrf "Failed to create valid extension"

I’ve repeatedly tried to connect two surfaces using connectsrf. I’ve recreated the surfaces several times. I’ve tried extrude, I’ve tried planes. Nothing has worked. Every time, I get the message “Failed to create valid extension.”

I’m certain that these surfaces are in the correct orientation to each other, ie that a connection could possibly occur. I’m not asking Rhino to do the physically or geometrically impossible.

Would anyone know why, please?

Without a file, anything is just speculation. Please post your 3dm file here.