Have just bought a Eye-fi Pro x2 8GB+Wi-Fi, First insert and test with camera it work fine and happy with it .
Whenever after take out from camera and put in a card reader came together with it and insert into computer,
when insert back to camera it will show cannot create folder, have to format the card with camera again and again in order
to get it work . my 550D camera fireware version 1.0.9
have anyone encounter this problem.