After a new installation of Windows 2003, the following class was missing. The problem was that everything was deployed on it and a re-installation was not a solution. After doing some googling, I have found WMIDiag utility and it gives me the way to repair it.
Don't stop the WMI service and delete the repository folder, it is NOT a solution. WMIDiag is the proper way to do it.
Please be aware that when you set the ExecutionPolicy in PowerShell on x64, you must change also in PowerShell x86 (particulary if you execute the scripts from a x86 editor). I have lost a lot of time because I have forgotten that my script editor was not a x64 version. When you find this kind of stuff, you said "OK, it is very logical, behind the scene, it is a modification of a registry key" and x64 OS keeps a special key "Wow6432Node" for x32 programs mappings.