Oh good to hear that the emulator works finally 
openFrameworks installs himself automatically to sdcard. That's why you should use "preferExternal" on the real devices. The emulator can work with "auto" because it is configured like that by its own implementation. But your Nexus5 without a sdcard can not run your app. Plug a sdcard then try it again.
So at least everything is clear now, isn't it?