I brought down the backend with the command:

/etc/init.d/mythtv-backend stop

When I try to bring it back up with:

/etc/init.d/mythtv-backend start

I receive an error: Unable to set initgroups() with gid 105

I am not sure what would cause this: I was stopping \ starting the system last night and did not observe this behavior. Has anyone observed this?

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R7.3: 0.22.20091023-1, Hauppauge PVR-500 (Philips FQ1236A MK4), Gigabyte Gigabyte EG45M-UD2H, E5200 2.4Ghz, 2GB RAM, NVIDIA GEFORCE 256MB

Sound like you were trying to do this as the mythtfv user rather than as root. Running init scripts is a privileged operation. The key shortcuts (alt-1 to start, alt-2 to stop, alt-3 to restart (stop and start)) use the sudo wrapper to accomplish this.