I recently came across this error while trying to amend the settings of a template.
I converted the template to a guest virtual machine, and found the settings were greyed out, while the below error message was displayed.
This appeared to affect all templates created before a recent vSphere 4.0 – 4.1 upgrade.
- Ensure the guest virtual machine is powered off
- Note the datastore location of the guest machine
- Right click on the guest machine and click "Remove from inventory"
- Navigate to the datastore noted in step 2
- Right click on the guest virtual machine config file (.vmx) and click "Add to inventory"