Image must be equirectangular 2:1 aspect ratio spherical ONLY.
That is: Exactly twice and wide as tall. 2500x1250, 4000x2000, 6000x3000 etc. If you cannot produce 2:1 image you should drop it on a 2:1 canvas and limit the tilt value. (not sure it's possible with Panorama2Flash as I don't have the program).