I had the same problem, here is how I found out what VM was causing it:
Ran this query off of the 1/2 upgraded database and found the VM with mem that was NULL
Once I had that I tried to find the name by moref ID.
SELECT TOP 1000 [id]
,[vc_id]
,[computer_name]
,[storage_allocation_mb]
,[validity_status]
,[guest_os]
,[is_vrouter]
,[is_published]
,[date_created]
,[template_id]
,[is_template]
,[needs_customization]
,[primary_nic_id]
,[guest_cust_vm_id]
,[guestos_id]
,[moref]
,[location_path]
,[cloud_uuid]
,[instance_uuid]
,[creation_status]
,[version_number]
,[suspend_proctype_id]
,[snapshot_moref]
,[dstore_moref]
,[ovf_env]
,[ovf_env_transports]
FROM [VCLOUDDB].[dbo].[vm]
where moref = 'vm-8971'
It gave me the name of the VM and it's ID, the problem was the ID was not in vCenter so I had to dig through the vCloud UI until I found a machine that matched it, deleted it and after that the upgrade ran smoothly.
Hope this helps someone!
