Put the card back in the camera and hit preview... if they're all fine, then it's the card reader... You can transfer from the camera via usb cable. If they are corrupt, then as Neuro said, alas it seems like a corrupt or worse faulty memory card. If your friend has a 2nd card, that should eliminate the source. Try reformatting the card, writing some shots and reviewing to eliminate the card. If a 2nd card has the problem, ideally different brand, then sounds like a weird fault on the 1Dx....
Oh and check pins in the slot that none are bent....