When I play a combination on my NS5R, the sound doesn´t stop sometimes although releasing the keys. Then I have to Mute the chanel to send a note off. Does anyone else has this trouble?

I've got no problems playing combinations on mine. Are you sure it's not a dodgy MIDI cable? Are you running through a sequencer? If so try connecting direct from your kbd. to NS5R and see if that solves it. It maybe your MIDI interface (if of course you're using a sequencer).
Hope you get it sorted
Ben