I have had something similiar with 3 cpu's last year. I suspect its a firmware problem.
1st of all you need a usb programming cable. Then switch power of to the cpu. Then remove the sd-card from its slot and power on. After it has loaded then push memory card back then only will you be able to connect. Then download the program to the sd card and toggle power again for cpu to load the new program (Download only if you have the same problem as me listed below)
Has this program been running for a while or is it a new program downloaded?
What I found to be the cause of my cpu freezing was that the cpu locked up everytime I switch an output coil on with no address (internal memory).
I did the above whilst removing a section of code everytime and downloading until I found the section. And all 3 times it was because of what I mentioned.
Schneider also couldnt help me until I found one tech that had the same problem