See if you have badblocks
. If I understand correctly, there is no date to care about now on this flash card so you can do destructive test with badblocks
. Don't worry. It will NOT destroy your flash card (it shouldn't!)> it will however destroy data on this flash card.
badblocks -wvs /dev/flshacard
Of course your dd
test was similar... It looks like something is not right. You could try different (USB?) flash card reader.