LUN sharing for Stornext VM's

I am trying to virtualize several of our (W2K) server that are using a Stornext filessystem. Several VM's need to share the 4 LUNs for their 2TB Stornext X: driveletter.

This is the setup:

ESXi 4.1 on a Dell R710.

QLogic HBA (QLE2462)

MDS 9120 (NPIV enabled)

HP EVA 5000

Stornext 4.1.2

First  VM with 4 RDM disks (NPIV enabled)

Second VM with 4 re-used disk with the above RDM  (NPIV enabled)

I have succeeded in getting 1 VM to use the Stornext filesystem, but as soon as I start the second VM, I get an locking error.

Reason: Failed to lock the file.
Cannot open the disk '/vmfs/volumes/4f755c4e-35026f64-c30b-bc305bd3fa63/Stornext Test/Stornext Test_1.vmdk' or one of the snapshot disks it depends on.

Anybody got any ideas how to avoid the locking, so that I can have the LUNs on more than 1 VM?

How can I be sure the LUN is mapped to the Virtual WWN?