Hi
Have a look at:
Might be because you are using Windows XP?
If you are I would suggest looking at a machine running Windows 7 or 8? And install the client there. See if it works?
Had this same issue at client sites before when working off old Windows XP machines.
I user server 2003 R2 std
if you are trying to access from windows 2003 or 64 bit xp, you need to apply windows hot fixes which is mentioned in the 5.1 release documents. please refer to https://www.vmware.com/support/vsphere5/doc/vsphere-esx-vcenter-server-51-release-notes.html and take a look on topic Search fails and Hardware Health and Health Status plug-ins are disabled in the vSphere Client
I install follow this step already
For Windows Server 2003 32 and 64bit, or Windows XP 64bit , apply the appropriate Microsoft hotfix: