When DPM does an upgrade of the agents it will ask for a reboot of the agent system. In some cases the server will be a production server that cannot be rebooted at that specific time.
There is a way to get around this and let DPM resume the normal backup routine without rebooting the specific system.
On the agent system DPM will create a registry key
HKLM\Software\Microsoft\Microsoft Data Protection Manager\Agent\2.0\RebootRequired
Delete that specific key and DPM will ignore the request for a restart.
In some cases the DPM agent will update its service or system-files for a new version.
Please make sure to plan the reboot in the near future to avoid DPM crashing from fixed bugs or known issues. Microsoft does not advise or list this workaround for obvious reasons.