Make sure that all components on the vSphere network have their clocks synchronized. If the clocks on the machines in your vSphere network are not synchronized, SSL certificates, which are time-sensitive, might not be recognized as valid in communications between network machines.

Unsynchronized clocks can result in authentication problems, which can cause the installation to fail or prevent the vCenter Server Appliance vpxd service from starting.

Make sure any Windows host machine on which a vCenter component runs is synchronized with the NTP server. See the Knowledge Base article http://kb.vmware.com/kb/1318.