I am running Data Protection Manager 2007 on Windows Server 2008 (x64).  I have not been able to use the reporting piece, and haven't been running DPM long enough to wonder much about it, but when I went to finally figure it out the answer was rather simple.  If you want to fix it, the answer is here, but for more about what the problem is, you can go to the forum post below.

This problem occurs because of a new permission requirement in IIS 7.0. This
permission requirement is for ISAPI extensions that use a wildcard (*) script
mapping.

To work around this problem, follow these steps:
1. Click Start, click Run, type inetmgr, and then click OK.
2. In Internet Information Services (IIS) Manager, expand Web Sites, expand
Default Web Site, and then click the virtual directory for the report server.
3. Under Features View, double-click Handler Mappings.
4. Under Actions, click Edit Feature Permissions.
5. Click to select the Scripts check box, and then click OK.

How to fix--- Data Protection Manager error 3013  SQL reporting tab  ? in Data Protection Manager

I have a few machines that have been retired (or just died) before I could uninstall the Agent.  I have been trying to figure out how to remove the agent name from the list, but every time I do a search, all I come back with is how to uninstall it from the client machine.  Well today I finally figured out what I should have seen earlier.

If you right click on the computer name in the list on the Agents tab and select uninstall a task view comes up.  Click on "Uninstall Agents" and the "Enter Credentials and Reboot option" dialogue comes up.  At this point you have to enter valid credentials and choose a restart option.  When you hit ok, and the machine no longer exists you will get a message similar to the following:

Click on "Yes" and the task list comes back and removes the DPM agent from the database.  And that means no more ghost entry for that machine.

I use DPM to backup a few servers, in a pilot group, and I was trying to add one to a protection group.  I kept getting this error every time I tried to modify the protection group to add another server:

Modify protection group: *Protection Group Name* failed:
Error 360: The operation failed due to a virtual disk service error
Error details: Unknown error (0x80042420)
Recommended action: Retry the operation.

I couldn't figure out the problem until I saw a post on this that mentioned there could be a problem using RDP.  Then I remembered that I can never do disk configuration unless I use a console session.  In order to configure disks it seems you have to be in "Session 0".  If you have to do this remotely, using "mstsc /console" for XP or 2003, or "mstsc /admin" for Vista will put you in "Session 0" just as if you were sitting at the console.