I've had some other random errors (Like the shuffle option not changing from off) all of which have been cured by power off and reboot...
Maybe that's what it was in the first place...

Jazz
(List 112, S/N 00030, 4 gig blue)
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Jazz (List 112, Mk2 42 gig #40. Mk1 4 gig #30. Mk3 1.6 16v)