The VSS services on the guest VM are not working properly.
This error is usually caused by one or more Windows VSS services being disabled. To fix it, you will need to go to Start > Run, and enter "services.msc" (without quotes). Here, you will see a list of services, their description, and whether or not they are running. Make sure RPC service is up and running.
You may also check the user who starts the service (the user specified in Veeam job for VSS connection).
Check that services are enabled and providers are operating properly.
To resolve this issue, check that the COM+ Event System service is started and that the Volume Shadow Copy service (VSS service) and Microsoft Software Shadow Copy Provider service are both enabled. You should also make sure that third-party installed VSS providers are operating properly. If a VSS provider is not operating properly, you should try reinstalling it. If that does not work, you should contact the provider vendor.