Disconnected NICs on VM

We have vCloud Director running many organisations and many VMs without a problem but every once in a while (after a reboot) a VM will lose it's network connection, vCloud shows the nic as connected but looking at the vDS (and properties of the VM) it shows as disconnected/link down

Sometimes we can fix this by vMotioning the VM onto another host but today we have one that just will not connect, we have tried:

• Restarting the VM
• Removing / readding the nics
• Using different adapter types (E1000/VMXNET3/Flexible)
• Stopping the vApp

I've seen this KB article but it has not resolved the problem:

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2061991

Is anyone able to suggest anything which may help?

Thanks

Marc