Do the following to troubleshoot this issue: 1) Check the spelling of the computer name. 2) Verify that Windows Server 2003 ...

Do the following to troubleshoot this issue: 
1) Check the spelling of the computer name.
2) Verify that Windows Server 2003 with Service Pack 1 or later is installed on the computer.
3) Verify that you entered the fully qualified domain name for the computer.
4) If the computer has recently been added to the domain, you may need to wait for Active Directory to update.
5) If the computer was recently restarted, wait a few moments and then retry the agent operation again.
6) Verify that a two-way trust is enabled between the domain that the selected computer belongs to and the DPM server's domain, and that the trust is of type forest.