Are you seeing this error when you try to back up your VMs with Veeam Backup & Replication 6.5 in Direct SAN Mode? Does your Proxy Servers sees the VMFS LUNs where you are fetching the VMs Data to the Backup Mode?
This error is generated because the Veeam Configured to backup VMs via Direct SAN Access “Using source proxy VMware Backup Proxy [san] and the Proxy doesn’t have access to the VMFS LUNs.
To sort out this issue;
1. Make sure your Proxy Server can see the VMFS LUNs inside the Disk Management of the Windows.
2. Make sure the Proxy configured as Direct SAN Access.
3. Make sure the Direct SAN Access Proxy is selected in the Backup Job Configuration / Storage Section.
4. If you are still getting the error and failing to process the backup further, Open the Proxy Configuration under Backup Infrastructure -> Backup Proxies and select the desire proxy.
Right Click on the Desired Proxy and Select Properties in the Selected DataStores, select the VMFS LUNs which contains the target Backup VMs manually and try..
Hope it helps..