DR4000 mount NFS from ESXi host

We have been given a Dr4000 to test with, our aim is to use VMWare's VDR product to backup our large datastores.

Therefore we need to mount the DR4000 as an NFS datastore to allow VDR to see/write to it. I have configured the DR4000 for both CIFS and NFS and can see and write to the CIFS side of things from Windows fine.

In VMWare I am attempting to mount NFS and I'm coming up against an issue. 

After I attempt to mount the store [SERVER : 10.11.89.240   -   FOLDER : /containers/backup/vmware] I get a error:

Call "HostDatastoreSystem.CreateNasDatastore" for object "datastoreSystem-5896" on vCenter Server "SERVER20.local" failed. 

NFS mount NATTHDR4X:/containers/backup/VMWare failed: The mount request was denied by the NFS server. Check that the export exists and that the client is permitted to mount it.

The NFS container is configured like this :

You will notice in the error message that I am attempting to mount to /containers/backup/vmware. This is a folder I created. however I have tried to mount the data store directly to /backup, I have created alternate containers and attempted to mount the datastore there.

I have tried with Insecure ticked and unticked. I have also 'Mapped root to :' all three of those options.

I have checked that the VM host has NFS services installed and firewall options are enabled and set to allow access to/from any host (See here : http://blog.jeffcosta.com/2011/01/10/hostdatastoresystem-createnasdatastore-for-object-ha-datastoresystem-error-when-setting-up-vmware-nfs-data-store/) 

I can reach the DR4000 from the VM host (ping the DR4000 hostname seems ok).

Any thoughts on how this can be configured?

Thanks,

Patrick