Need help with new Blu-Ray player and stereo receiver.

Hopefully someone here can help me, I bought my parents a blu ray player for xmas but I am having some problems with it. I am trying to hook it up to a LG LHT874 system, which has HDMI Input and Output. Then it goes to a projector. When I hook it up normally there is no sound coming out. I figured out that if I have the Blu-Ray player playing something with audio then I turn off the receiver, unplug both the HDMI Input and Output cables, then turn on the receiver plug in the input then the output cables I will get audio to work, until the blu-ray player stops putting out audio, ie end of a movie. I think that the must be different audio formats between the two or something. Any ideas on what might be going on or how to fix it? Many thanks.