Unexpected error

public bool Play()
        {
            //Run until all invaders are dead or an invader reaches the end.
            int remainingInvaders = _invaders.Length;

            while(remainingInvaders > 0)
            {
                //Each tower has opportunity to fire on invaders
                foreach(Tower tower in Towers)
                {
                    tower.FireOnInvaders(_invaders);
                }

                //Counr and move iinvaders that are still active.
                remainingInvaders = 0;
                foreach(Invader invader in _invaders)
                {
                    if(invader.IsActive)
                    {
                        invader.Move();

                        if(invader.HasScored)
                        {
                            return false;
                        }

                        remainingInvaders++;
                    }
                }
            }
        }