Browsing through your KBs, I couldn't relate to my issue of the moment.
I have 10 devices working perfectly in my network. An 11th one however, will not display WMI sensors, but there is no error message. Ping, SMTP, whatever other sensors work just fine, and WMI sensors work fine on other devices, but on this one the WMI sensors remain gray and with the following message insite the portal:
Starting Sensor (results for this sensor type can be delayed for several minutes at system startup. Please wait)
WMI service is running, RPC too. I can hit WMI from another device in the network.