Twice recently I've received permission to fly near an airport - directly in the flight path - as long as I stayed under 200 feet. However, when I tried to fly the first time my Mav hit an invisible wall. It would not fly across that invisible border that marked the flight path. It simply stopped forward motion when it came to that map line. In a similar situation, after receiving permission, I was already in the flight path, about three miles from the airport. However, my Mav simply would not take off, and the controller returned the message "NFZ". In both cases, I was trying to do some low altitude real estate work and the control tower knew exactly where I was. Was the control tower operator in error? Or was I just foolish thinking I could fly into flight path with permission? Is there a work-around in this situation?