DS_COMM_FAILURE is a very generic error but it usually means the /etc/hosts file is mis-configured on either CA Performance Center or the Data Aggregator or both. Make the necessary changes to the /etc/hosts file and attempt to add the Data Aggregator again.
Another possible cause of a communication failure would be the firewall is running on one or both systems. Run the following command on each system: /etc/init.d/iptables status. If you get any output then run /etc/init.d/iptables stop to stop the firewall. Then attempt to add the Data Aggregator again