Having trouble with a rigging tutorial

I have been using blender for a few years, but only to create models and some textures for game assets. Thought it was about time to try out some animation and rigging

I have tried to follow Laustinarts Basic mechanical Rigging tutorial via Youtube
http://www.youtube.com/watch?v=4pWN3oGnNa4 And found it perfectly clear and understandable for an animation first timer but I’m not getting the same results

I’m all good till about 5.45. When I try to constrain the left arm it rotates with, instead of opposing, the right. It does oppose if I invert x, but either way everything to do with the left arm is borked from this stage onwards. I have compared it to the Final file but cant find any notable difference.



PBs_Basic_Mechanical_Rigging_Start.blend (671 KB)