Having the exact same problem.
Just bought the Clip Sport a week ago.
Put about 12gb of music on a brand new Patriot 64gb Class10 microdisk with no problems; the largest file being a 1.2gb audiobook. Files looked fine. Seemed to play fine.
Unplugged everything and went to use the clip sport about an hour later. When trying to get to the external drive I got “Disk Error Please re-plug SD card.” I tried unplugging/re-plugging 10-15 times - same error. I also tried to turn off the clip sport and re start, same error.
I plugged the clip sport into the computer and it says H drive (micro disk) needs to be formatted. I hesitated, but reformatted anyway since I had most everything backed up. After refromatting, the Computer found the drive so I created folders and put some music on it. Unplugged Sport Clip and tried to play music. And it says same error “Disk Error. Please re-plug SD card.”
I plugged the Sport Clip back into the computer and it says the card can’t be read and I need to reformat it again!