I came across the following problem a couple of times:

In VirtualCenter, when trying to delete a virtual machine that is switched off, VirtualCenter comes up with:

"Operation failed since another task is in progress"

Also, when trying to use the vmware-cmd command to START, STOP, RESET, SUSPEND or UNREGISTER on the Virtual Machine, the ESX Server responds with:

VMControl error -999: Unknown error: SoapError: ServerFaultCode(1520) : (vim.fault.TaskInProgress)

Yet, when issuing the vmware-cmd getstate command, the ESX Server responds with "Off"

SOLUTION:

The following solution has always fixed the problem for me:

Just execute the following command on the ESX Server:

service mgmt-vmware restart

NOTES:

• No Host Reboot or Downtime Required
• No Virtual Machine Downtime Required