Further investigation shows that there is nothing worng whith my box. this is a cubase problem.
Testing..
Conecting a Midi keyboard and a Sound module instead of the Midi box shows the following.
Key pressed on keyboard  MuteButton on mixer Turns On
Press keyboard again and the  MuteButton goes off, but no sound from the module ( the generic remote is set to Resive AND transmit)when Pressing the mute button with the mouse the sound module plays a note and holds it as long as the button is on. Correct.
Conclution: When resiving a midi msg. Cubase’s “Generic Remote” does not send a msg, out.
I remember that the generic remote of Cubase SX is not so well maintained by Steinberg like before. In particular versions one or two functions are not working, in following versions they are fixed but other functions are failing… :-/