You are backing up several virtual machines with Acronis Agent for Hyper-V (installed on the Hyper-V host) or Acronis Agent for VMware (Windows) installed on a Windows machine connected to the ESX(i) host.
The backup plan is applied to a group of machines.
In a while, you receive an error message or an email notification about the error:
Error code: 58
Message: No backup items were resolved: ('500EC4AF-FFF4-A630-17E6-FBB30CFD4DC3','mms::vm::machine') GXT: The item provider has skipped the report of an item with key '('500EC4AF-FFF4-A630-17E6-FBB30CFD4DC3','mms::vm::machine')'.
This error means that a virtual machine was disconnected (deleted or migrated) from the original host, while it is still listed in the backup plan.
This is a known issue with agentless backup of virtual machines; the backup plan is not automatically revoked once the machine is no longer present in the environment.
Revoke and then re-apply the backup plan to the host.
The issue will be fixed with one of the future releases.