This is a known issue affecting
VMware vCenter Server and vCenter Server Appliance 6.0.
Currently there is no resolution.
To workaround this issue, install all intermediate CA certificates (including the VMCA Root certificate if in use as a Subordinate CA) in the Trusted Certificate Authority store of the Operating System while accessing the vSphere Web Client.
This operation will vary depending on the Operating System. Please engage your Operating System Support Organization for more details.
Refer these articles for Windows and Mac OS X:
Note: The preceeding link was correct as of September 02, 2015. If you find the link is broken, please provide feedback and a VMware employee will update the link.