Check services.msc and ensure that the Event Services and Volume Shadow Copy service are started on the Agent machine.
Verify in the Event Viewer application logs for any VSS errors and consult the following documentation regarding their event ID: http://technet.microsoft.com/en-us/library/cc734545(v=ws.10).aspx.
Ensure that your Windows OS is up-to-date with the latest updates from Microsoft. Double check the Microsoft KBs for any hotfixes related to VSS for your OS.
Restarting the following VSS services may correct the issue:
Sometimes, re-registering the following VSS DLLs from a command line prompt will help resolve VSS problems.
Once the DLLs are registered, reboot the server. If any DLL cannot be registered, reboot the server and register the DLL again.
For more information please follow the link:
http://social.technet.microsoft.com/Forums/en-US/b3e3fc4a-c142-4220-95c1-f69a7624f426/error-0×80042318-vss-when-trying-to-create-a-restoring-point