Can't rotate an GameObject...

Hi,

i want to make a GameObject flying around passing some waypoints. On its way it should face the waypoint it its heading to.

This worked fine with this script:

     void FixedUpdate()
    {
           transform.position = Vector3.MoveTowards(transform.position, WP[actPoint].transform.position, speed * 10);
         transform.LookAt(WP[actPoint].transform);
         
       if(isNearlyThere()){
             actPoint++;
             
             speed = UnityEngine.Random.Range(minSpeed, maxSpeed); 
             
             if(actPoint >= WP.Length)
                 actPoint = 0;
                 
         }
    }

But suddenly it stopped rotating. I even cant rotate it with for example transform.rotate(0,90,0) - what happened? "WP" is an Array of empty GameObjects which act as waypoints.

Can you help me out?

Thanks!