Cannot add an existing virtual disk

I am trying to make a Network load Balancing Cluster on a GSX server 3.1, and i am using the guidelines from the Administration Guide. I make the First Node and ran sysprep on it. I then renamed (from NLB01 to NLB02)and copied the VMDK files (NLB02.VMDK and NLB02-flat.VMDK)to a directory called "Cluster", just like it says in the manual, but when i try to "add an existing disk" i recieve this error message.

Failed to retrieve disk information for "E:\Cluster\NLB02\NLB02-flat.vmdk":

The file specified is not a virtual disk.[/b]

Then i tried the same with the other VMDK file "E:\Cluster\NLB01\NLB02.VMDK" Same error message.

What am i doing wrong.

Thanks in advance