Cannot create a virtual machine in a datastore on a networked nas

Hi,

I'm running Vmware server 2 on a Windows 2003 R2 host.

I'm trying to create a Windows 2008 guest on a networked NAS (a WD MyBook II) with 2048 GB RAM, 75 GB disk, but after I click "Finish" on the wizard I have the error:

Create virtual machine failed to complete

Details: Unable to access file. MyVM/MyVM.vmxf

The datastore is CIFS, and works (.iso is inside). but I have this error anyway.

I have to notice that during definition I had to use MyBook/administrator instead of administrator alone or server\administrator. The first works, the other two didn't.

BTW, installing on a local disk works fine.

Any hint?

Thanks