Hi,
there's a KB, especially for that: http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2036350
The KB suggests this hotfix: VMware ESXi 5.1, Patch ESXi510-201212402-BG: Updates tools-light
The patch fixes the issue. Impact: none. Just roll out the hotfix with UpdateManager.
Cheers,
Frank