Command lego power functions with arduino and scratch.

Hello I have the project to pilot a lego power functions with an IR led. It is controlled by scratch through the arduino.
I managed to control the lego thanks to a "sketch" on the arduino and I also managed to control the arduino (lighting a led) with S4A 1.6.
But I can not control the lego from scratch through the arduino.

I saw a video on youtube and some links that proves that it works.

Equipment:

I connected the GND from the IR to the GND of the Arduino and the VCC to the output 5.

Http://heppg.de/ikg/wordpress/?p=771
Http://conoroneill.net/check-out-scratch-for-arduino-s4a-easier-electronics-for-kids/

Thank you for your help