Getting error transform.position assign attempt for "Player" is not valid on rigidbody

I've seen others ask about this error and some say it appears in the editor only, some say it's because 1 or more of the Vector3 values is null.

I can see in the debug that my project thinks the x and z values are null - but I don't understand why, this is a rigidbody and I don't calculate the Vector3 through my code. I use AddRelativeForce() & AddRelativeTorque()

This error occurs when my player hits a wall in a specific part of a specific level. Could it be related to the bounce texture I have on my level mesh maybe? Honestly got no idea.

Edit: kmgr wanted to see code so here's the most relevant bit. Like I said, I don't edit the Player's transform directly. Only the rigidbody.

 function FixedUpdate () {
 
     var moveHorizontal : float= Input.GetAxis ("Horizontal");
     var moveVertical : float= Input.GetAxis ("Vertical");
     
         if((moveHorizontal < 0) || Input.GetKey("a"))
         {
             GetComponent.<Rigidbody>().AddRelativeTorque (0,-rotationSpeed,0);
 
         } else if((moveHorizontal > 0) || Input.GetKey("d"))
         {
             GetComponent.<Rigidbody>().AddRelativeTorque (0,rotationSpeed,0);
         } 
         
         if ((moveVertical > 0) || Input.GetKey("w"))
         {
 
             GetComponent.<Rigidbody>().AddRelativeForce (Vector3.forward * speed);
 
         } else if ((moveVertical < 0) || Input.GetKey("s"))
         { 
             
             GetComponent.<Rigidbody>().AddRelativeForce (Vector3.back * speed);
         }
 }