Thanks for the update; the large UI is the key, it is what's causing the crash you are getting. To help you be able to trade credits, there are two options.
I'll attach an updated version of the screen file that is causing the trouble. You can use that file and replace the one you find in Steam/SteamApps/common/Galactic Civilizations III/Screens with it, then go to common/Galactic Civilizations III/Tools and double-click the "ScreenDataCompiler.bat" to update your screen data. This way you can keep running the game with large UI enabled, and you should be able to pop up that popup without it crashing anymore. As a note, though, if you verify your Steam files or otherwise reinstall or update it, you will have to follow these steps again because the changed file will be overridden. This will be fine when our next patch comes out, because it will include this fix anyways.
Alternatively, the crash does not occur if you run with small UI instead of large UI. Doing this in general may also fix some places where our large UI does not work or look its best yet that you may have noticed already. If you have it on large UI because of a very high res screen or the text otherwise being too small, you can try running in lower resolution and scale things up that way, if you don't mind the blurrier map.
Sorry you ran into this issue, hopefully one of these solutions helps you until the next patch comes out.