Ensure that the first event here is the first event on the brick, or the Enabled parts will not work. You might also need to adjust things if the event you want needs a delay, using relays/etc.
Enabled - Delay 0 - onPlayerTouch - [DO WHATEVER YOU WANT]
Enabled - Delay 0 - onPlayerTouch - Self - setEventEnabled - [0], [Disabled]
Enabled - Delay 0 - onPlayerTouch - Self - cancelEvents
Enabled - Delay 400 - onPlayerTouch - Self - setEventEnabled - [0], [Enabled]
The event should call once when a player touches the brick, and not be called again until players move off the brick.