Problem Flipping Pose on X-axis


I am just starting out with blender and I have just finished rigging my character. :slight_smile:
Blender file:

I have started doing some poses and then when I use ctrl+shift+v to paste the opposite pose, stuff starts going haywire and I don’t know what is going on or how to fix it. I have been playing around with the rotation of the bones but to no avail.:no::spin:

PS Also any critique on what I have done would be great.:wink: