You say "you need HDMI cable connected". Meanwhile, i experienced exactly opposite. Customer had 612 connected with HDMI and mirror TV connected to coax output. HBO channels would give him this message on mirror Tv unless main TV (HDMI connected) was on. Solution was to replace HDMI with component+optical.
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This is where we are seeing the issues. It's happening to people who have a receiver outputting to two devices. Unhook the one and it may take care of it or swap out the HDMI cable with Component cables.