Your .psd file should operate the same way a solid will work.
The process you describe appears to be correct.
However, you might want to remember a couple of things about copy/pasting mask path data to position data.
Try one of these?
Turn off your camera in your scene. Does your .psd layer appear to follow the path when the camera is off?
Create a Null. Copy & Paste the same data. Does the Null follow the path correctly? Is it possible that the anchor point for your .psd layer has been edited?
Is the 3D layer not facing the desired AUTO ORIENTATION along the path? Adjust the Orientation values for the layer. It will still auto-rotate with the path direction, but with your custom orientation values.
Maybe this will help. Instead of using the camera has the target of your paste use a null or a solid or any other layer.