Error "Account AccountName can't define the cpmdata policy, as it's not the owner of the CPM Server" may be displayed when creating the "cpmdata" policy.
This means that you are trying to create the "cpmdata" policy using an account that isn't the owner of the CPM instance.
In order to find the account that owns the CPM instance, please open the instance's properties in the EC2 Console.
Check the "Owner" field - it will contain the account number.
Using that account's Access Key and Secret Key, you can create an Account in CPM.
This account will be able to create the "cpmdata" policy.
Additionally, this can happen if the volume ID of CPM's data volume has changed. A whole log bundle search for "cpmdata" may quickly find an error like this in the logging:
2019-03-19 09:55:52,710: ERROR: check_cpmdata_policy_eligibility_and_get_capacity(aws_utils.py:1049) account AccountName failed to get volume vol-0bdbb5385b879dfbf. Exception: The volume 'vol-0bdbb5385b879dfbf' does not exist.
In this event, something has caused the volume ID of the data volume to change in a way that CPM doesn't know about. CPM is attempting to find the volume to create the cpmdata policy and cannot. The fix is to terminate this instance of CPM and launch a new one, properly attaching the data volume within the initial configuration of CPM as detailed here under "existing data volume"