Originally posted by Steve.Ledger I've seen this before and it's always been a faulty card.
Agreed its a classic case of BAM corruption (block availability map) as this only happens on user file systems it point ineringly at the SD card
If it was the buffer failing it would be a lot more random.
The data is correct just not re-assembled
Not looked at this recently but a quick fix under fat used to copy the seconadry File allocation table over primary.
I'd not format that SD card but thow it in the nearest trashcan or use it where data has no value.