Scanning is the process in which you generate compliance information about the vSphere objects against attached baselines and baseline groups. In some cases, the scan of ESX 4.0.x and ESXi 4.0.x hosts might fail.
The scan process of ESX/ESXi hosts might fail.
If the VMware vSphere Update Manager Update Download task is not completed successfully after you add a host to the vSphere inventory, no host patch metadata is downloaded.
After you add a host or a virtual machine to the vSphere inventory, run the VMware vSphere Update Manager Update Download task before performing the scan. For more information, see Run the VMware vSphere Update Manager Update Download Task.