What has the one to do with the other? MarvinKosh provided this information so you can get your game files back to vanilla status without having to completely reinstall the game.
Your tech tree problem stems from a syntax error in your modded files (probably a typo or missing line). I had similar errors in my mod too.
As I said before, the easiest way to solve this, would be for you to either upload your mod, or to post your changes. Without more information, however, I find it quite difficult to help you.
At the very least, answer me this: Are all races affected by this, or only one? If all are, then the error is in the TechTree.xml. If only one is, then the error is most likely in the racial tech tree of that race.