Saitek X-55 issue: button 15 pressed

Hello,

I've just started setting up my X-55 but I cannot make the stick working properly, while the throttle is perfect.

This is my problem:

Button 15 seems to be always pressed, but in fact there are no button pressed and I even don't know which button is! As a consequence, no buttons in the stick work, while axis are functioning.

Does anybody has some advice for this? I made everything according to what the manual says: download and install the latest drivers, plug in both USBs and then install Saitek Software, but still no luck ...

Thanks