- Check if the Windows Management Instrumentation Service is running with the Computer Mangement Console.
- Start dcomcnfg from Start->Run.
- Open properties from Component->Services->Computers->My Computer.
- On the Default Properties tab check that DCOM is enabled.
- On the COM Security tab compare the settings with a maschine on which WMI works.
- Also go to Component->Services->Computers->My Computer->DCOM Config->Windows Management and Instrumentation node and also check the security settings within the properties dialog there.
If WMI is still not accessible you can download the WMI Diagnosis Utility and check the affected hosts. If all target hosts expose the same WMI error you may also want to check WMI on your own machine.