Failed to connect to ACS: Could not resolve host

I added a new cpe and I configured it correctly.
unfortunately I could not detect it on ACS and here is the message in the CPE log “Failed to connect to ACS: Could not resolve host”

Can you help me solve this problem. just for information, the IP ranges that I use in the CPEs are private IP ranges.

Regards,

If the CPE has the option or a shell, you should be able to ping the ACS from the CPE.