I have a Dell PowerVault DP600 running Data Protection Manager 2007 on a Windows Storage Server 2003 R2 OS. The unit was delivered by Dell in this configuration. It has worked wonderfully for years, backing up XP, Win 2003, and Win 2008 servers. I have recently added a Dell PowerEdge T710 server running Win2008 R2 functioning as a file server. The DPM can't see this machine in Active Directory to deploy an agent. The agent was manually installed on the new server by mapping the DPM server's C:\ and installing from the DPM server without error. The new server is still not listed in the DPM. Is there something else that needs to be checked for the server to get listed in DPM?
I remember at one point in time there was a specific service pack or update required to get 2007 to work with 2008 R2 and Windows 7 boxes. I'll see if I can find the link but make sure your DPM box is fully patched.
Applying the hotfix from here fixed the problem. I'm not sure excactly what the problem was to cause this, as the description of the issues in didn't describe what was happening.