Welcome to the forum
Check this KB
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=100200...
if it doesnt help chk the below,
1) Edit the settings of the virtual machine, click the Options tab and make sure that the guest operating system version is correct. This can cause this error, so make sure you select the correct OS. E.g. “Microsoft Windows Server 2008 R2 (64-bit)”.
2) Try removing the virtual machine from the vCenter inventory and re-adding it.
3) Try restarting the VMware management agents (service mgmt-vmware restart and service vmware-vpxa restart).
Award Points if helpful!!