[Hampshire] SD Card Problem

Whilst trying to understand my camera problem, (discussed elsewhere,) I
found that I had an unco-operative 512Mb SD card. Neither of my two current
machines (ThinkPads, Etch and Gutsy) would acknowledge its existence, using
either of my two plug-in SD card readers.

I had repeated the test many times at intervals over a week and was about to
consign the card to the landfill bin, when something prompted me to try once
more with the same card readers on a much older, half-forgotten ThinkPad
with W/98 installed.

It worked perfectly. I was able to retrieve the photographs from the card
and re-format it. This (Etch) machine then mounted it immediately and it
seems now to be reading and writing faultlessly.

I'm mystified. Can anyone suggest an explanation?

Chris.