Hello,
What is the error message you receive when attempting the backup or update?
Generally speaking there are a few common issues:
* Make sure you have specified the correct management VRF for the device in iMC. This is under Configuration Center > Options > VPN Instance tab. Select the device and then specify the VPN Instance (VRF) name that you use for management.
* CLI access needs to be working correctly for the devices in iMC. Ensure the 'Login Type' for the device is set correctly and that iMC has the correct credentials. There's a Test button on the SSH/Telnet settings window you could use to verify this.
* Transfer protocols TFTP and SFTP_SERVER are the only currently supported ones for AOS-CX in iMC. Ensure iMC is configured to use one of them with the AOS-CX devices. This can be configured on the Configuration Center > Options > File Transfer Mode tab.
* You could try to delete and re-add one of the devices to iMC and see if that helps. This will force iMC to redetermine the adapter (scripts for backup/restore etc) to use for this device now that it recognizes it - it's possible the adapter did not update automatically after you upgraded and the device got recognized.
Hope that helps.