I have been using the transmitter at home for a long time with a pair of Panasonic RB-HF420B headphones. I have now bought another set with a Hama transmitter and two identical headphones for a holiday flat. Now it works with one pair of headphones, but the second pair cannot be paired. When I try to pair the new headphones at home, it doesn't work either, but the headphones from home work fine with the transmitter in the holiday home. Where is the worm?