This may happen because the it is very easy to double tap the Auto Brightness Adjust box in the notebook manager, so it gets unchecked and then checks right back again.
To fix the problem open the Notebook Manager (the button which looks like two gears to the right of the screen) -> go to the Advanced Tab -> uncheck the Auto Brightness Adjust box. Wait for a moment to make sure is is unchecked and click OK to exit the menu. Now you can adjust the brightness to the desired level manually.
You can adjust the brightness manually in the "Common" tab of the Notebook Manager.
Keywords: brightness, SL10, Slate, 2GO Pad.