losing signal to center channel and subwoofer

I'm switching between stereo and surround modes. For instance, if I switch from 5-channel stereo to 5-channel surround, I will lose the center and sub. Also, I can switch between various stereo channels and subsequently lose the signal when I go back to 5-channel stereo.

I called B&K and was advised to reset the processor which I did, but that didn't solve the problem. It appears worse now. I haven't been able to get anything from the center or sub all day. Usually I could just switch the system off and regain those channels, but now that doesn't appear to work.

Thanks fo rthe responses. All speakers are selected and set to small in the menu. The speaker configuration is the same for each mode(stereo,surround,thx). I briefly got the subwoofer to come on, but as soon as I switched modes I once again lost the signal. The center channel is still dead.