There is no way this is from a fresh install, you had to have changed something with the folders. Try reinstalling and DON'T do anything to ANYTHING! (Considered by the fact that you cannot load your base folder)
I.do.know.what.I.am.talking.aboutIt is an instillation error or something he did. Renders why his Blockland won't read anything from his base folder.......
Ok, try going to C:\Program Files\Blockland\base\ui\ and see if there is a BlockWindow.png file in there.