For info: the only times I have seen this message have both been sorted by ensuring good IDE cable connection (by pressing it down hard again

One was not long after an upgrade, but the other appeared to be unconnected to anything, so my assumption is general day to day bumping wiggled the connector slightly loose.
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Rory
MkIIa, blue lit buttons, memory upgrade, 1Tb in Subaru Forester STi
MkII, 240Gb in Mark Lord dock
MkII, 80Gb SSD in dock