It is wanted that for scrolling down, you have to put the mouse to the very bottom so the mouse can click on the buttons on the bottom part which appear if you select something. To select something, simply click (left mouse button) on it (for example a villager). Then a click with the right mouse button chooses the target for the villager (a tree, a building which is not finished yet or simply a free space to move (for every kind of unit). Clicking on a building results in having the unit move into the building (bug)). After selecting a villager, you can also choose a building to build. You can also select more than one unit by drawing a rectangle around them (press and drag the mouse). I will add it to the description how to select and move. Thank you for pointing that out.

Since highscores are in fact working online, you can consider adding one which shows the score for each player. (Or at least the first place which is me now) :P

The game is working. Open this scenario: http://www.greenfoot.org/scenarios/12380 Do you get a red screen? You might want to look at this discussion http://www.greenfoot.org/topics/8200/ and follow the steps.