Flatten Harness Components - Assemble all greyed out

Hello,

I'm new to using this software and although i have already managed to do this once now i can't.

I have the 3D model with the connectors and i have already routed the cables but when i try to make a manufacturing harness and try to assemble the components (connectors) the "assemble" and "Assemble All" options are greyed out.

Do you have any ideia why?

Thanks you