Hi Lee,
there can be several reasons why CCS Manager can't contact (ping) the agent, please check following:
1. your CCS manager can resolve the agent name
2. you can reach agent on port 5600 from CCS Manager. I advise using portqry tool and run following command from CCS Manager: portqry.exe -e 5600 -n <agent fqdn or ip>
3. If you have created sites, ensure that correct CCS Manager is contacting the agent (via routing rules). You can check this by right-click on asset (not the agent) and selecting Evaluate Routing Rule.
Hope this helps.