Misconfigured RPC Settings cause Backup Job to fail with "Failed to prepare guest for hot backup"

This KB is only relevant when all three of the following errors occur.

The Task Summary displays:

Failed to prepare guest for hot backup. Error: Cannot upload guest agent's files to the administrative share [\\...\ADMIN$]. Cannot copy file. Source file: [..\VeeamGuestAgent_X__.exe]. Target file: [\\...\ADMIN$\VeeamVssSupport\VeeamGuestAgent.exe]. CopyFile() failed. Win32 error:The process cannot access the file because it is being used by another process. Code: 32

The Task Log Contains the following:

Veeam Guest Agent is not started   at Veeam.Backup.Core.CViGuestInventoryInformer.IsEnabled()
   at Veeam.Backup.Core.CViGuestInventoryInformer.Veeam.Backup.Core.IGuestInventoryInformer.TryToInventory(CGuestInventoryInfo& inventoryInfo)
Cannot upload guest agent's files to the administrative share  [\\...\ADMIN$].
Cannot copy file. Source file: [..\VeeamGuestAgent_X__.exe]. Target file: [\\...\ADMIN$\VeeamVssSupport\VeeamGuestAgent.exe].

The VeeamVssSupport Service is Hung within the Guest OS

Check the VeeamGuestHelper log found in C:\ProgramData\Veeam\Backup Contains

            Updating Windows Firewall exceptions list.. Ok.
            Registering RPC protocol sequences used by the server.
            Registering RPC protocol sequences used by the server.. Failed.
ERR         Cannot register RPC protocol sequences used by the server.
ERR         Cannot force RPC run-time library to use all supported protocol sequences for receiving remote procedure calls.
ERR         RPC error:The parameter is incorrect.
ERR          Code: 87

This issue occurs, when RPC settings have been customized and are not properly configured in registry.

By default the HKLM\SOFTWARE\MICROSOFT\RPC\INTERNET key does not exist, if it is presented it must have been created. Likely, it was created by someone reviewing the information found here, or another article discussing that specific registry key.

Remove RPC Customized Settings:

1. Log on to Guest VM
2. Open the Registry Editor (regedit)
3. Navigate to HKLM\SOFTWARE\MICROSOFT\RPC\INTERNET
4. Export the INTERNET key to back it up.
5. Delete the entire INTERNET (and it's sub-keys).
6. Reboot the Guest, run the Veeam job again