Veeam ONE triggers “Failed to open VM attachment”
alarm when the following Windows events are registered on the Hyper-V host:
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).