The Virtual Server Start VM action will start a stopped (or saved) Virtual Machine, or (optionally) resume a paused Virtual Machine.
Virtual Machine Property Page
See the Virtual Server overview topic for details.
"Resume Paused Virtual Machines"
If this option is selected and the target VM is paused, it will be resumed.
"Fail if the Virtual Machine is already running"
If this option is selected and the target VM is already running, the action will fail. Otherwise, it will contain.
"Action waits until the Virtual Machine has started up before continuing"
Once the signal is sent to start the stopped VM, it can take some time to start up (especially when saved.)
If this option is selected, the action will not continue until the Virtual Machine is up and running. If you are not accessing the Virtual Machine immediately, you can disable this option.