Hi clever people

I have a cluster with 2 hosts running ESX4U1, all managed by the latest version of vCenter Server. Licenses: Enterprise Plus

I 'm trying to get the Nexus 1000V to work.
I have installed the VSM successfully and the hosts are updated with the latest version of the VEMs.

In my vSphere client,  when I go to Inventory > Networking, I can see my new Nexus DVS OK. When I try to add the hosts to it everything seems fine. The hosts have exactly the same network configuration with 6 physical uplinks, 4 of which I dedicate to the N1kV.

The port configuration on the physical upstream Cisco switches are setup identically. They all allow my test VLAN (183).
The VSM vnics (management, control, packet) are set on 3 individual port groups all on VLAN 183.
Each host service console talk to each other on VLAN 183 too.
I let VUM add the VEMs automatically successfully (I also did so manually in consecutive tests)

When I add the first host to the DVS, I can see the module loading on the VSM fine:
DVSN1kV-DBY2# 2010 Mar  3 04:17:00 DVSN1kV-DBY2 %PLATFORM-2-MOD_PWRUP: Module 3 powered up (Serial number )

sh module
Mod  Ports  Module-Type                      Model              Status
---  -----  -------------------------------- ------------------ ------------
1    0      Virtual Supervisor Module        Nexus1000V         active *
3    248    Virtual Ethernet Module          NA                 ok

Mod  Sw               Hw     
---  ---------------  ------ 
1    4.0(4)SV1(2)     0.0   
3    4.0(4)SV1(2)     1.10

Mod  MAC-Address(es)                         Serial-Num
---  --------------------------------------  ----------
1    00-19-07-6c-5a-a8 to 00-19-07-6c-62-a8  NA        
3    02-00-0c-00-03-00 to 02-00-0c-00-03-80  NA      

Mod  Server-IP        Server-UUID                           Server-Name
---  ---------------  ------------------------------------  --------------------
1    10.100.18.43     NA                                    NA
3    10.100.18.0      44454c4c-5a00-1047-8059-c6c04f4d344a  vmh01-dby2.*******

So far so good, however, when I add the second host, I get:
2010 Mar  3 04:17:05 DVSN1kV-DBY2 %PLATFORM-2-MOD_PWRUP: Module 4 powered up (Serial number )
2010 Mar  3 04:17:12 DVSN1kV-DBY2 %PLATFORM-2-PFM_VEM_REMOVE_NO_HB: Removing VEM 4 (heartbeats lost)
2010 Mar  3 04:17:12 DVSN1kV-DBY2 %PLATFORM-2-MOD_REMOVE: Module 4 removed (Serial number )

As you can see the module loads and gets kicked out straight away.
I have been trying to debug this to no avail. I have followed the 'getting started' and 'troubleshooting' guides found on the Cisco site but cannot find what the problem is...

I attached a file with more output from various debug commands I got from the troubleshooting guide.

I'd grately appreciate if someone could find the time to help. It might be a but more obvious to you guys!

Thanks in advance.

Raph