trim/extend - can only use weldment bodies

when i try to trim/extend a weldment using a thin revolve as a trim/extend tool, i get the error "only  bodies created by Weld Member Feature can be used"

i swear (in more ways than one) that i have used the exact same bodie ins this model to trim/extend weldments.

am i crazeee?

SolidworksWeldments