Guys, its easy.. I found a little piece of paper after seeking calmly. It was on the paper pulling system when collecting from the tray. See the pic, it was right whee i'm pointing with my tool. It was locking one of the sensors around there. See in the third image where my tool is pointing.. Its exactly inside and very difficult to see.. And one more thing.. You'll have to unscrew the upper cover to see it.. Good luck
I love smart gadgets like this. Easy to solve.