Hi,
Before the issue happened, was there any changed made on the windows client, such as windows update or hotfix installation?
Please run "get-hotfix" in PowerShell as administrator to get the hotfix list installed recently.
If no change has been made, you might need to uninstall the server essential connector, unjoin and rejoin the domain and then reinstall the server essential connector. After that, test if the backup can be successfully completed.
Thanks,
Eleven
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