We had the same issue with the status when downloading patch definition - 'scanning virtual appliance'
I also found the same fail to lock vm-xx error in C:\ProgramData\VMware\VMware Update Manager\Logs\vmware-vum-server-log4cpp.txt
[2012-04-19 13:54:03:358 'InventoryTree' 4100 ERROR] [InventoryTree, 137] Timed out while acquiring the lock for vm-286
[2012-04-19 13:54:03:358 'InventoryTree' 4100 WARN] [InventoryTree, 1636] Failed to lock vm-286; Timed out
Sure enough as several have posted, this was due to VMA applicance preventing the scan. Once powered down the scan completed first try after restarting the VUM service. Thanks to all who have contributed to this thread.
Is there any fix as we have the latest VMA and 4.1U2 builds. I'd rather not have to schedule a VMA power down during the scans..