A flight could not be prepared

[Larkspeed]

All of a sudden I am getting this error no matter what I set for flight parameters

[Steve Waite]

This normally suggests that a "compatible" airport is not nearby your present location, within the flight time available.

Flight gen page:
You may need to increase the desired flight time.
You may need to choose the full scenery airport list instead of a subset.
You may need to uncheck some filters, ILS means an airport without ILS will not show.

If these fail:
Can you go to the map and manually choose a destination then?
Can you get a flight by changing location or aircraft?

Regards;
Steve

[Steve Waite]

Another thing to check:
Look at the Aircraft Flight Parameters, Range, Cruise Altitude, and so on. See all the values make sense.
regards
Steve