In tip 7261 » When you open a security policy related MMC snap-in, you receive 'Snap-in failed to initialize', I explained that this behavior was symptomatic of NOT having the %SystemRoot%\System32\WBEM folder in your PATH environment variable.
This behavior will also occur if your PATH environment variable ends with \.
To resolve the problem
1. Right-click My Computer and press Properties.
2. Select the Advanced tab.
3. Press the Environment Variables button.
4. Double-click PATH in the System variables area.
5. Remove the \ from the end of the string.
6. Press OK and OK.