Basically, the vCenter Workflow Manager service had stopped on my vCenter server. In my case, I’m running the 6.0.0 vApp so I had to open an SSH session and enter the following:
– shell.set –enabled true
– service-control –status vmware-vpx-workflow
(this command confirmed the service was stopped)
– service-control –start vmware-vpx-workflow
Once running, I was able to start VMs again from vCenter.
Not sure why this was so hard to find in a web search but hopefully the search engines will pick up this blog post and save people some time!