Confusing error messages, !IsNormalized and NxRay direction not valid

I am getting weird errors from my script, I do not understand why. I have looked up these errors but I can't find anyone who has gotten it for the same reason. Most other people have gotten the errors from lens flares on their cameras which I don't understand. The errors are:

1. NxRay direction not valid: must be unit vector. UnityEngine.Physics:Linecast(Vector3, Vector3, Int32)

2. !IsNormalized (ray.GetDirection ()) UnityEngine.Physics:Linecast(Vector3, Vector3, Int32)

3. !IsNormalized (dir)

This is the bit of code it is from I have commented on the line of the error.

 void Cover()
     {
         Vector3[] covers = new Vector3[100];
         List<Vector3> potential = new List<Vector3>();
 
         NavMeshHit navhit;
 
         for(int i = 0; i < covers.Length - 1 ; i++)
         {
             NavMesh.FindClosestEdge(transform.position + Random.insideUnitSphere * 5, out navhit, passableMask:1);
 
             covers[i] = navhit.position;
             if(Physics.Linecast(navhit.position, sensors.eyes.playerPosition, ~mask) ) // Error happens on this line
             {
                 potential.Add(covers[i]);
             }
         }
 
         if(!hascoverpos)
         {
             hascoverpos = true;
             chosen = potential[0];
 
         }
         if(!Physics.Linecast(chosen, sensors.eyes.playerPosition, ~mask) ) 
         {
             Debug.Log ("Recalculating...");
             hascoverpos = false;
         }
 
         print("Potential Covers = " + potential.Count);
         print("All Covers = " + covers.Length);
 
         TargetDestination = chosen;
     }

Can anyone help me? thanks