Definitely an SDL2 error.
From a different programs same error:
3) Down load SDL 1.2.15.dmg (Intel 10.5+) or if you are an older version (Intel 10.4+)
http://www.libsdl.org/download-1.2.php
and also SDL2 2.0.3.dmg (Intel 10.5+)
http://www.libsdl.org/download-2.0.php reason being I downloaded them both and not sure which one it uses but it works so just download them both.
4) (this is the step that took me forever to figure out.) The SDLs go in the Library on your finder. If you can't find your library I am about to tell you how. You first go to finder, second you mash command+shift+g and it will take you to a box you can type in, so third you type this ~/Library
guess what you are now in your Library (for future ease do what this kid tells you at the end to do
it makes it easier to reach in the future.)
5) Now that you are at your library you will have to create a new folder and you must name it Frameworks if not the program won't find it.
6) Move both SDLs into the new folder (all you need is the lego looking object.)
http://forum.simutrans.com/index.php?topic=14010.0