Try this work around
check the vcenter ip address is listed for hosts file go to the vcenter machine location below c:\windows\System32\drivers\etc\hosts and add the vc ipadress there eg: 192.168.0.20 virtualcenter.domain.com virtualcenter reboot the vcenter machine after the change and this will fix the issue.
If still issue, try the latest update VMware-VIMSetup-all-5.1.0-1235309.iso