Rebuild Performance Counters

If nagios was working OK and then suddenly you get lots of errors similar to :

UNKNOWN - The WMI query had problems. You might have your username/password wrong or 
the user's access level is too low. Wmic error text on the next line.
[wmi/wmic.c:196:main()] ERROR: Login to remote object.
NTSTATUS: NT_STATUS_ACCESS_DENIED - Access denied

You may need to rebuild the performance counters on the machine that cannot be queried.

This is detailed on https://support.microsoft.com/en-us/help/2554336/how-to-manually-rebuild-performance-counters-for-windows-server-2008-6 but to summarise:

Open a administrator CMD window

To Rebuilding the counters:
     cd c:\windows\system32
     lodctr /R
     cd c:\windows\sysWOW64
     lodctr /R

To Resync the counters with Windows Management Instrumentation (WMI):
     WINMGMT.EXE /RESYNCPERF

Stop and restart the Performance Logs and Alerts service (only if it is running)
Stop and restart the Windows Management Instrumentation service (this should always be running)

If all this fails, you may have to reboot