Plasma tv/home theater. I have a panasonic plasma tv model No.TH-50PX600A[50in] connected to a

Question

I have a panasonic plasma tv model No.TH-50PX600A[50in] connected to a panasonic home theater system model No.SC-PT850W using a hdmi cable, every thing seems to work perfectly except when I try to play tv sound through the home thearter i get no sound I.E. I go to menu on tv go to sound highlight "home theater" and then enter this turns home theater system on them mutes tv sound,[sound levels are turned up of course]