Hi, I successfully installed the game and the GECK, I successfully created a small mod. I can open the mod in the GECK, but not in the game. the .esp file is NOT listed in Data Files of the loader, nor is the mod present in the game, but the GECK is able to load and save it without problems...

I modded Morrowind, Oblivion and Skyrim a lot, and never had this problem...