Sandro, the problem isn't something unusual - you made a mistake while calling packages. For Unreal engine in .zip you sent me there are two files called "Ha" (no matter what is their extension) and Unreal engine tries to load one with .u (and you get that error).
Never call packages with the same names! Is it name.utx or name.u or name.uax or name.dx, it doesn't matter for the engine.
So, just rename your map to something different