From the command prompt, type DPMAgentInstaller.exe dpmservername to install the protection agent on the protected computer. ...

From the command prompt, type DPMAgentInstaller.exe  [dpmservername] to install the protection agent on the protected computer. Then attach the protection agent to the DPM server using the Protection Agent Installation Wizard. 
OR
 Verify the following: 
1) %ServerName; is online and remotely accessible from the DPM server.
2)A firewall if enabled on  %ServerName; is not blocking WMI requests from the DPM server.
3) The WMI service on %ServerName; is running.