I would copy the files off the Card onto the PC, then format the card on PC, then format the card Via the pc.
Transfer the files back from PC to card and try exactly the same thing again.
If it happens again I would say the card is screwed.
Is it a Scandisk by any chance ?
I ask because I have heard of a few 1gb Scandisks that become screwed.
Better the card is broken than the PSP though eh
