You may see following problem if you login vCenter Server 6.0 by vSphere Client:
Login to the query service failed.
The server could not interpret the communication from the client. (The remote server returned an error: (500) Internal Server Error.)
That’s because “Use Windows session credentials” checkbox is selected. Deselect it and give it a try.
Refer KB Searching the Inventory with the vSphere Client fails (2143566)
