If you use your Mac to download and copy to the card, those invisible files are the resource forks for the jpegs. Your Mac does not show them, but the TV sees them and then stops the Slide Show because they are not readable. I have seen various solutions to wipe those files off the SD card or USB drive, but with my Snow Leopard OSX, they did not work. I did this:
1. Erase and Format the SD card for Fat32.
2. Write the files onto the blank card or drive from my PC laptop. No hidden files, so plays perfect.
3. If you have another OSX maybe the suggestions for using the 'Clean' commands in the Terminal will work.
4. Check this link on how to clean those files. http://superuser.com/questions/319553/mac-terminal-script-to-remove-hidden-files
...That my friend worked to perfection...cannot thank you enough for taking the time to help me out...Cheers!