Some of our hosts were with the error "Quick stats on hostname is not up-to-date".
This is know issue in 5.0 and 5.5, that is fix in the updates, but in vCenter 6.0.
The workaround to fix this issue is to add this quickStats parameters to the Advanced Settings of vCenter Server:
So lets add this paramenters to the vCenter Advanced Settings.
Connect to your vCenter using vSphere Client and go to Administration > vCenter Server Settings
Add the first key in(vpxd.quickStats.HostStatsCheck) and add a value "False"
Click "Add" and then add the second parameter(vpxd.quickStats.ConfigIssues).
After adding both parameters, restart your vCenter Server services.
Then all messages should go away and the problem is fixed.
Note: For a more detail information about this issue, please read KB-2061008 from VMware
Hope this article can you help fixing this issue.