ah wait, are you using a 3rd party to auto start MIDI Translator? aren't you using a third-party app to put it in a tray? And the settings image error only happens when auto started?
Yes, MT internally uses such a PNG file as an icon in the settings dialog. It seems to be the first image to be loaded. Chances are that all other icons would fail, too, but MT already bails out on the first failed image. MT does not look pretty without icons! The icons are in the program itself, so it's kind of strange that they're not found. The only thing I can imagine is that the "current directory" at start of the program may need to point to the program folder.
Sorry for your various problems... at least they're new and fresh problems

Regards,
Florian