Well, I found one more bug and one thing I'm not exactly sure what to make of it.
The bug is, that the program doesn't recognise if a tech is set to a different Category in the racial tech tree than what it is in the main tech tree.
For example, I set the fleet module and Terror Star techs to Category Null in the TechTree.XML. I set them intentionally to an invalid Category to prevent the AI from researching those techs. While it doesn't really do that, it at least slows the AI down. For the Korath, I set those techs to Category Invasion, because that makes definitely sure, that they will never be researched. The program, however, still reports, that those techs are set to Null in the Korath tech tree.
The thing I'm not sure about is this:
Der Objektverweis wurde nicht auf eine Objektinstanz festgelegt.
Roughly translated it means: The object-link hasn't been set to a object-instance. This message shows up several times, when testing the PlanetaryImprovements.XML. I'm not sure, if this means, that there is a bug in my file or if there is something wrong with your program.