The CF card is not passing validation, there's something wrong with the card's data. If you are using windows 10 with the fall update to write out your cards, that's the reason it's not working. In the fall update, microsoft in their ever infinite wisdom has decided to write a 4 byte ID code on each removable device to keep track of it for it's indexing service. So anything you put on a windows 10 machine with the fall update will have this 4 bytes written to it, thus trashing the card as far as slot play is concerned. You need to use windows 8 or 7.
Also make sure your OS/Bios combination is correct.