I was trying to push back in this Mango 737-800, and had disconnected all ground services. While they were disconnected, I was finishing up filing my flight plan. After a solid 90 seconds, I initiated my push back, after checking that all ground services had cleared, and got this message.
That’s happened to me. One time I was about to fly a long haul, and had a very specific departure time. It wouldn’t let me push and I had to end the flight. It sucks.