I have a Windows 2008 Server currently monitored via PRTG using mostly WMI sensors. All sensors are fine except the Pagefile Usage sensor. See below:
I have followed the first suggestion found here: https://kb.paessler.com/en/topic/35963-80041010:-the-specified-class-is-not-valid without any success. The second is a bit harder follow as there is no specific service associated with the pagefile WMI that I can think of in order to check the registry.