I bet the card corrupted while copying those files over. If you have a backup of the data on the 8gb card (presumably, still on the 2gb card?), I would try the uber-panasonic formatter: http://panasonic.jp/support/global/c...formatter.html

Warning: I have never used this software, but have heard many people say it brought their card "back to life".

Concerning the second issue, your tablet will always mount it's SD Card slots on the computer, even if there is nothing in them. That is not strange at all.