Model group won't allow me to place any families

[roedigerF6NSW]

I have an As-Built model, supplied by an outside firm, which is missing one window. Within the As-Built model, the buildings adjacent to our site are modelled and grouped, yet I'm unable to add anything into the groups. Every time I place a window, draw a wall, etc. I get the following error message- anyone know whats going on? 

 

[azad.Nanva]

i think you should draw the wall or curtain wall out side the group and then use add to group.

you should just choose the curtain wall, the mullions and the curtain panels and grids is the part of curtain wall.