Thanks for the reply, but I still can't get it to work.
#This works when I select everything with a mouse
#I have the transform "t" defined elsewhere
model = Sketchup.active_model.selection Sketchup.active_model.active_entities.transform_entities t,model
......
#I tried this to select everything without the mouse, but it does nothing
model = Sketchup.active_model.selection.add(Sketchup.active_model.entities)
Sketchup.active_model.active_entities.transform_entities t,model