Here is a quick fix for those experiencing a problem using VMotion after upgrading from ESX Server 2.5 to ESX Server 3.5

In some cases after this upgrade is done VMotion is disabled and warm migrations are not possible. The solution is to re-enable VMotion on the host.

Re-enable VMotion on the host:

1. Select the host in VI Client and navigate to the Networking section of its Configuration tab.
2. Click the Properties link for the switch associated with the VMkernel port.
3. In the switch Properties dialog box, select the appropriate network label and click Edit.
4. Select the VMotion Enabled checkbox and click OK.