Veeam ONE triggers
“Failed to open VM attachment” alarm when the following Windows events are registered on the Hyper-V host:
12290 Microsoft-Windows-Hyper-V-Worker
12290 Microsoft-Windows-Hyper-V-SynthStor
12290 Microsoft-Windows-Hyper-V-VMMS
12140 Microsoft-Windows-Hyper-V-VMMS
12140 Microsoft-Windows-Hyper-V-Worker
12240 Microsoft-Windows-Hyper-V-SynthStor
These events are logged when the Hyper-V host or the Cluster node cannot access some of the VM virtual disks, configuration files, virtual memory, saving state or snapshot files.
NOTE: In most cases, this happens when the files are located on the shared storages (for example CSV or SMB shares).