Just got this blog setup today and wouldn't you know it there's somthing to talk about already.
We've had a problem recently with multiple (1000's!) of 'WMI Probe Module Failed Execution' alerts for workflow SQLServer.2005.AgentDiscovery. The specific error was 'Invalid Class'.
The SQL installation seemed sound so it was puzzling that WMI queries against the SQL class were failing.
A quick google round some SQL sites revealed that apparently SQL Server 2005 installations can sometimes leave SQL WMI provider improperly installed, leading to WMI queries failing to enumerate SQL objects with the same error. the good news is that you can easily fix this with a Microsoft utility called 'Mofcomp.exe', bundled with SQL Server 2005.
Just run C:\Program Files\Microsoft SQL Server\90\Shared>mofcomp "C:\Program Files\Microsoft SQL Server\90\Shared\sqlmgmproviderxpsp2up.mof". You should see a message that ends with "..Storing data in the repository...Done!"
Now slightly less noisy....
Steve