Cheap card on Ebay. Alarm bells.
Does your Mac have some kind of disc-checking utility? Card could be defective if files are switching around like that.
Worse, flash cards are often counterfeited.
Make sure you have copies of all your music somewhere other than the card, because to test it you’re going to have to overwrite it.
Borrow someone’s PC again and get H2testw
http://www.softpedia.com/get/System/System-Miscellaneous/H2testw.shtml
Run it and see what it tells you about the card.
Also, you should get rid of all the Mac “finder” files that are 0kb and start with ._ and end with mp3. There aren’t good ones and bad ones. The Sansa doesn’t know what to do with any of them.
You could sort by size and get rid of all the 0kb ones. You can also delete (from the Sansa, not your Mac) any folders labeled MACOSX, which is where those finder files usually are.
