Your firewall may be blocking Blockland from creating/deleting/replacing files, or might not have administrative access to do so. (I think moving the folder to Documents fixed this, though)
Alternatively, check your console for any errors that might surfacing. It should show in-game by pressing the tilde (~) key, and is also open as a command prompt-style window behind the main game.
Activating the console tracer can show a wider range of what problems there may be, I believe you can do so by entering trace(1); in the console. Correct me if I'm wrong.