Symptoms

Operation (backup, recovery, cleanup) fails with the following error:

Windows error: (0x8007051F) There are currently no logon servers available to service the logon request

Example of full error log: click to expand

Error code: 4194350
Fields: {"$module":"disk_bundle_vsa64_23094","path":"smb://backup/acronis/PC02/","user":"Backup1"}
Message: Failed to open the backup location.
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Error code: 262145
Fields: {"$module":"disk_bundle_vsa64_23094","function":"NtOpenFile","path":"\\\\?\\UNC\\-backup\\acronis\\"}
Message: Error occurred while reading the file.
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Error code: 65520
Fields: {"$module":"disk_bundle_vsa64_23094","code":2147943711}
Message: There are currently no logon servers available to service the logon request
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Cause

In the network, there is a running Active Directory domain controller, which should be processing the user login request. Windows on the machine where the error reproduces has not found the domain controller and does not allow you to log in. Possible reasons:

1. The domain controller is not activated in the network.
2. The machine or the backup destination(e.g. NAS)  gets a wrong DNS IP address: it should be the IP of the domain controller in the same network.
3. DNS server does not have a valid IPv4 (either IPv4 127.0.0.1 is used or IPv6 ::1)
4. Other DNS-related issues

Troubleshooting

• Make sure that the machine is connected to the network with Domain Controller
• Verify that the domain controller is available and working properly. Ensure that the Netlogon service is running on the domain controller.
• Clear DNS records cache: Open Command Prompt: start -> search -> type "cmd". In Command Prompt, issue:
  ipconfig /flushdns
• Check DNS settings in network connection properties: 

Press Win+R, then type ncpa.cpl and press Enter to open Network Connections window. Right-click on the connection that represents your internet/active network connection and select Properties. 
In network adapter properties window, click on the TCP/IPv4 item, and then the Properties button. This will open a window that includes a section for DNS settings. 

Workaround

As a temporary workaround, you can use credentials of local user that has read and write access to the backup destination.