Thank you Dominika, I was feeding it back into a parameter of the object as a quick way of debugging and I think that triggered a loop of some description. Breaking the loop solved the problem.
…we also tried to call the ArchiCAD internal object of gs_general_window_macro in the exact same way Rectangular Opening 19 did: call "gs_general_window_macro" parameters all iWindowClass=4, iWindowType=26
I beg your pardon, I meant Double-Hung Window 19. The two iWindow variables are for Double Hung windows.