Veeam: ‘Failed to open disk for read’

Problem EVERY VMware Job in Veeam failed with the following error, (for every Guest VM); Processing SERVER-NAME Error: Failed to open VDDK disk [[DATASTORE-NAME] SERVER-NAME/SERVER-NAME.vmdk] ( is read-only mode – [true] ) Logon attempt with parameters [VC/ESX: [ESXi-SERVER-NAME.DOMAIN-NAME.COM];Port: 443;Login: [[email protected]];VMX Spec: [moref=vm-231];Snapshot mor: [snapshot-288575];Transports: [san];Read Only: [true]] failed because of the following errors: @Failed to open disk for read.[…]