Problem with terrain brush.

I just reinstall my Window 1 month ago. Then I downloaded and installed the last version of Unity Free, and now I notice that I can’t choose any brush except the first one of the list, as you can see in the screenshot, even I change the type of brush and brush size, it doesn’t work at all.
P/S: I had reinstalled Unity and, nothing change. And thank you everyone who answer my question!alt text

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Well, remove Unity, reinstall the newest version and make sure you use the right version for your OS (for example, Window 64-bit or 32-bit). That should work.