possibly the while loop is running before ZUG get filled, or after ZUG is destroyed.
Try this
Code:
   while(1) 
   {
      if((me!=0)&&(you!=0)&&(zug!=0)) 
      {
         vec_for_vertex(my.x,you,87);
         vec_for_vertex(zpos2.x,you,87);
      
         vec_for_vertex(zpos1.x,zug,41);
         vec_for_vertex(zpos2.x,zug,41);
      
         vec_lerp(temp.x,zpos1.x,zpos2.x,0.0);
         vec_diff(temp.x,temp.x,my.x);
         vec_to_angle(my.pan,temp.x);
      }
      wait(1);
   }


"There is no fate but what WE make." - CEO Cyberdyne Systems Corp.
A8.30.5 Commercial