I advise you do the following before you go to CAS EEPROM reading.
1- Go to key programming, and check if CAS EWS5 is active or not (if Not jump to 4).
2- If EWS5 active, please check if you can read DME ISN by OBD.
3- If you cannot, check if it is Bosch or continental, if Bosch, then you can use the tricore boot mode to read the ISN. If Continental... forget about it (at least for now).
4- Read EEPROM from CAS
5- Use Autohex II to complete the bmw key programming procedure . if EWS5 is active you will be asked to input the DME ISN.
You can do nothing when CAS4+ got a corrupted EEPROM. the only solution after that is buying a new CAS.