You select a Windows NFS server as backup destination in Where to back up.
Backup fails with this error:
Failed to lock archive.
When backup starts, Acronis product creates a new archive or opens an existing archive to start/continue writing a backup into this archive. For this time, access to the archive must be granted to Acronis process while restricted for other processes (this process is called file locking or byte range locking). Some NFS servers on Windows cannot always correctly process file locks which causes backup failure. This error indicates the issue with file locking on your server.
Use NFS server on Linux as they show a more stable performance or switch from NFS to another protocol like SMB.