Thanks for your reply.
I managed to do it as I descibed with a couple of VMs before these 3 VMs. I got a bit surprised that suddenly it didn't work out.
Since the Labmanager SAN with it's ESX host and vCD SAN with it's ESXi hosts are on different iSCSI VLANs we can't connect both vCenter ESX/ESXi servers to same LUN. But it might be something to look at.
I'm now in the process of Consolidating the 3 VM's in Labmanager and then do a new OVF of them and try again.
/Tony