"Cannot convert argument to Geom::Vector3d" error

[Pixero]

I get a: "Cannot convert argument to Geom::Vector3d" error and I can't see what I'm doing wrong here:
Code snippet:

sel.each{|e|
		tr = e.transformation
		ip = tr.origin

		xa = tr.xaxis
      ya = tr.yaxis

      a_vector = Geom;;Vector3d.new(a_center.x-ip.x, a_center.y-ip.y, 1)

      if(@@axis == "X")
			obj_axis = xa # I've tried with this...
			obj_axis = Geom;;Vector3d.new(xa) # ...this...
         obj_axis = Geom;;Vector3d.new(xa.to_a) # ...and this
		elsif(@@axis == "Y")
			#obj_axis = ya
			obj_axis = Geom;;Vector3d.new(ya.to_a)
		end#if		
		
		angle = a_vector.angle_between obj_axis ### ArgumentError; Cannot convert argument to Geom;;Vector3d
                # do more stuff here...
}

[TIG]

Before the line starting angle...
Add in these to see what the arguments you pass are

out the possible obj_axis permutations and retest...

` p e
p tr

p a_vector
p obj_axis

p a_vector.to_a
p obj_axis.to_a`

If one or both of them are NOT vectors, then we've got somewhere...