Network I/O and Disk I/O spinner are greyed out (4246223)

When select a Virtual Machine the Network I/O and Disk I/O spinner is greyed out. Both spinners are working fine when opening a Virtual Center, but for Virtual Machines and ESX Hosts it is greyed out (see attached screen shot SpinnersGreyedOut.jpg)

For any reason some derived metrics are lost.

To check if the derived metrics are available:

1. Go to "Administration | Data | Manage Derived Metrics"
2. Enter the search key "HostStorage" in the "Derived Metric Scope" field and make sure the derived metrics are available - see attached screen shot DiskMetrics.jpg
3. Enter the search key "HostNetwork" in the "Derived Metric Scope" field and make sure the derived metrics are available - see attached screen shot NetworkMetrics.jpg

If the metrics are not available please disable and re-enable the Core-Hosts cartridge.

To disable and re-enable the cartridge:

1. Go to "Administration | Cartridges | Cartridge Inventory"
2. Select "Core Cartridges" in the field "Core Type"
3. Enter search string "host" in field "Cartridge Name"
4. Mark the cartridge "Core-Hosts" and click on "Disable Selected" and then on "Enable Selected"

Now check if the metrics are back. Wait few more minutes to the let the data collected/calculated correctly and check if the Network I/O and Disk I/O spinner is working ok now.