Are you sure you have connected your Ouverture with the BV10 via a Powerlink cable? You have to use a Masterlink cable. The Powerlink sockets are all outputs , not inputs. 

Stefan

I'm sorry. I mean masterlink instead of powerlink.

I'm not sure if this is effective in your setup, but did you check if your balance of your Ouverture is in the middle? 

Balance is in the middle. When I connect a headphone to the headphone out on the Ouverture the sound in the headset is o.k. So then the sound on left and right earphone is real stereo.

Connect the Beolabs directly to your Ouverture. If the sound is ok, I`m quite sure, the ML cable is faulty. The Masterlink has balanced signal, thre wires for right channel (2x signal, 1x ground) and three for the left channel. If one wire is missing, there will be a signal, but less volume and bass.

See also beotech Masterlink wiring.

Stefan

ML cable is already replaced. (see 3rd reply)

But I think Stefan is on the right track. It is possible that one pin in the ML-socket is bend to the outside, not making contact with the ML-plug. Likely this happened on the BV10, because that socket is harder to reach than the side on the Ouverture. You might want to take a look at that.

With Beolabs direct to Ouverture the problem is still the same, so I think it has to be the Beosound Ouverture (output on headphone is o.k.).

I think so too. Maybe a contact problem with the headphone socket, or the mute relay not working properly. I`d plug - unplug the headphone several times, and if this doesn`t help press the mute button several times. just a guess....

Stefan