veeam backup error：
6/12/2016 3:29:01 PM :: Processing vm-01 Error: VDDK error: 1 (Unknown error). Value: 0x0000000000000001
Failed to read from a virtual disk
Failed to upload disk.
Agent failed to process method {DataTransfer.SyncDisk}.
Exception from server: VDDK error: 1 (Unknown error). Value: 0x0000000000000001
Failed to read from a virtual disk
Unable to retrieve next block transmission command. Number of already processed blocks: [10].
Failed to download disk.
cause： maybe the Host connect problem
KB：
https://forums.veeam.com/vmware-vsphere-f24/repeted-vddk-error-1-and-2-t32723.html
We had the same issue - restarting the management agent on the host where the VM was housed resolved the issue (this only causes the host to be disconnected from vCenter for a minute or two but doesn't cause any downtime to the other VMs)
Backups have been fine since (2 days and counting)
solution：
migration the vms to other host
