Can't Copy Paste Mirrored Pose I am following this tutorial but when I reach this part part at 19:38 I press Ctrl + C it copies but when I press Ctrl + Shift + V nothing happens.

A little menu appears on the side with Flipped on X-Axis selected but the right side doesn't copy the left side.

What am I doing wrong?
In order to perform any kind of mirroring operation on your bones the names on the left and right side of your rig must have identical names, other than the L/R indication. All the bones on the right side of your armature have '.001' at the end of the names left over from being copied at some point. Remove the .001 from each of the names on the right side so they match the left side and you will be able to paste the pose mirrored.