Not really sure what causes this error all of a sudden, need to investigate more.
To fix this issue lets check the state of Host.
Host is running, but if you notice the summary page and look at the “Resources” section you will find the data for CPU / Memory Usage is not being pulled.
Another way is to “Remove” the host from vCenter and “Add” back again.
To remove the host, right click on the host and select “Remove”
This action will give a security alert, Click “Yes” to move ahead.
You can monitor the “Recent Tasks” for the status of your action.
Lets “Add” the Host again.
Right click on the “Datacenter Name” and select “Add Host…”
You will be prompted again with the Security Alert, Select “Yes” to move ahead.
Upon completion of wizard you can go through the summary once again.
And the Host will be added
Once the Task is complete, check the “Summary” page of the Host and check the “Resources” section.
Now try Powering On the virtual machine, and it should power on.