Hi Keith,
You could try something like File Salvage to recover your missing 4 minutes:
http://subrosasoft.com/OSXSoftware/index.php?main_page=product_info&product...
It's difficult to know whether it's a corrupt file directory on the card or the 4 minutes of video is actually missing. In any event you're not having much luck copying things back and forth because you're copying the corruption as well. Try the File Salvage trial version and determine whether or not the program "sees" the missing video. If it does then you may have some luck retrieving the clip(s).
Another way to go might be using the directory repair program called DiskWarrior (if you already have it) to rebuild the directory on the card. This is uncharted territory because I don't know if the program will rebuild a FAT32 directory, which is the SxS Pro memory card formatting. If you have DiskWarrior it might be worth a shot. DiskWarrior is a Mac-only program but it's very good at what it does. I went back in your history here at the COW and I see that you're a Mac/Final Cut Studio user, so you might already have this great program. If you go this route try rebuilding the directory on a copy of the BPAV folder first and not the original one on the card.
http://www.alsoft.com/DiskWarrior/index.html
I've been shooting to SxS Pro cards for over a year now and have never had an instance of losing video clips. When it's time to delete or empty one of my cards I do a reformat of the cards in-camera every 4th or 5th time instead of just dragging the files to the trash with a card inserted into my Macbook Pro. If you're having a continuing problem with just one of your cards even with good preventative maintenance then I would strongly suggest you return the card to Sony and get another one.
Oh, and make sure you always insert a card into your camera rather firmly to make sure it connects properly.
- Don
