I had read that you could delete clips from the SDHC card when the camera was connected to the computer. Just click on and delete the clips in the PRIVATE>AVCHD>BDMV>STREAM folder.
I tried that with a card with a single clip on it. When I ejected the camera and switched it to PB mode, it showed me something I'd never seen before. A "clip" that had a question mark icon on it. I couldn't play the clip. I couldn't delete it via the camera either. I figured the PLAYLIST folder on the disk must still have had the idea that the clip existed? (Not sure if that's how the camera works)
So like any naive and stupid person would, I decided to delete everything in the PRIVATE>AVCHD>BDMV>PLAYLIST folder too. Upon ejecting the camera and putting it into PB mode again, I got a horrible full screen error. "SYSTEM ERROR TURN POWER OFF". Well shoot.
So I did that, but I still had that error. I put in a new card to make sure it wasn't my camera. Luckily the new card worked. When I put the bad card back in, I was at least able to have it mount to the computer. but when putting it in PB or CAM mode, I got the error again.
So here's what I did, written like your favorite recipe.
1. Placed good card in camera
2. Mounted on computer
3. Copied the entire RIVATE>AVCHD>BDMV folder to the desktop
4. Ejected camera
5. Placed bad card in camera
6. Mounted on computer
7. Copied the entire RIVATE>AVCHD>BDMV folder to the bad card
8. Ejected camera
And the bad card now works. With one stipulation. While the card had always told me that there was 99 minutes of record time when empty, now the card says 98 minutes of record time are available when the card is empty.
So is 1 minute of footage still hidden in there? Do I have 1 minute of corrupted space? I don't know. And I don't plan to use this card for important projects unless I know it's fixed or it can be fully fixed from this point.
But in case this happens to you, hopefully this post helps.
Good to know, thanks. It's best practise not to delete stuff from the card through the computer, only use the camera's interface - there are metadata references, etc on the card that the camera knows about but you don't.
Now that the card works in the camera again, have you tried reformatting it? (Again... only in-camera.)