problems in duplicating a object/ creating a object through python API

Question

I created a city scene which has a vehicle model inside, I need to duplicate the vehicle model to display a dozen of them in the city scene through python API. The vehicle object name is BMWM1. I have tried on these two approaches Approach 1 from stackoverflow

scn = bpy.context.scene
new_obj = bpy.data.objects["BMWM1"].copy()
new_obj.data = bpy.data.objects["BMWM1"].data.copy()
new_obj.animation_data_clear()
scn.objects.link(new_obj)
new_obj.location = (-8, 6, 2)
scn.objects.active = new_obj
new_obj.select = True

Approach 2

bpy.data.objects['BMWM1'].select = True
new_obj = bpy.ops.object.duplicate()
scn.objects.link(new_obj)
new_obj.location = (-8, 6, 2)
scn.objects.active = new_obj
new_obj.select = True

Both approaches received a error saying

"warning DM_ensure_tessface: could not create tessfaces from 144 polygons, dm->type=2 warning DM_ensure_tessface: could not create tessfaces from 144 polygons, dm->type=2 "

And the second approach additionally received a error:

" scn.objects.link(new_obj) TypeError: SceneObjects.link(): error with argument 1, "object" - Function.object expected a Object type, not set "

I have also seen the tutorials like Three ways to create objects, two ways to create a new object

Add the data, and then the object. For a mesh: 

me = bpy.data.meshes.new(meshName)
ob = bpy.data.objects.new(obName, me)

and for an armature:

amt = bpy.data.armatures.new(amtname)
ob = bpy.data.objects.new(obname, amt)

While I tried another way

me = bpy.data.objects["BMWM1"].data;
me_copy = me.copy()
new_obj = bpy.data.objects.new("BMWM1",me_copy)

scn.objects.link(new_obj)
new_obj.location = (-8, 6, 2)
scn.objects.active = new_obj
new_obj.select = True

but still at the end the error

"warning DM_ensure_tessface: could not create tessfaces from 144 polygons, dm->type=2 warning DM_ensure_tessface: could not create tessfaces from 144 polygons, dm->type=2 "

happened again

I tried the duplicate again as commented by

bpy.data.objects['BMWM1'].select = True
set = bpy.ops.object.duplicate()

for new_obj in set: 
  scn.objects.link(new_obj)

still produced a error

scn.objects.link(new_obj) TypeError: SceneObjects.link(): error with argument 1, "object" - Function.object expected a Object type, not str