Disk device path not specified for RDM backing

Hi,

     I am currentlly trying to create  shared storage to use on a Microsoft cluster within ESX 5.1 environment. We are using a NetApp SAN (V3160 Series)

     When the LUN is created and attached to the HBA WWN on the ESX hosts, I then try to create a RDM disk and get the error once the finish button is pressed.

A general system erro occured: Disk device path not specified for RDM backing

any help would be appreciated.

Thanks