Very interesting thread,
I also sometimes get the invalid disk error on every disk, but only after a "off/on" after I've used gracenotes. It really looks like gracenotes screws up the machines program.
To fix this, I unplug the machine out of the mains, press the on button to drain the power supply, plug it back in and its all back to normal, nothing is lost. these days I use gracenotes sparingly, infact I leave it off the internet in normal operations.
One thing I've...