When the vCenter Server Appliance is joined to an Active Directory domain, it REQUIRES a reboot before it will operate correctly. This is displayed in the VAMI:

To avoid unexpected downtime, the Appliance does not force the user to reboot after configuring Active Directory authentication. I have seen several problems caused when users try to avoid this reboot entirely. This will cause the appliance to fail during certain Active Directory related Single Sign-On operations.
Pro Tip: Reboot the Appliance immediately after joining it to an Active Directory domain!