Please help. Panasonic viera link not working.

My current TV and stereo setup is as follow:-

Panasonic plasma TV TH50PZ850 (2009 June)
Panasonic home theatre system SC-PT470 (2009 Christmas)

HDMI cable connected to HDMI port 1 on TV, and Optical link cable run audio out of the TV into the stereo.

When I hook up both machine last week, everything works fine. I can control volume on my TV with the HT remote, and when I play the sound from TV broadcast throught HT, the speakers on theTV set would de-activate itself, and sound would only plays throught the HT speakers. Happy.

But, in the weekend, after a big tidy up, and when I hook everything up in the same way. The viera link started doing funny thing. Now, when I play the sound from TV broadcast throught HT, the speakers on the TV would remains ON, it no longer de-activate itself ? I would need to turn down the volume myself.

When I try to go into the viera function of the TV set to check for setting, it says this " service is not avaliable", even though I have trun on the viera link function in the setting menu.

However, other viera link functions seems OK, i.e I can still turn off the TV set with my HT remote, and change volume on the TV with my HT remote.

What gives ?

PS. I am very happy with the picture quality of the PT470. Much better than with my normal DVD player.

Many Thanks.

Happy New Year