How did you prevent Microsoft Management Console from handling MSC files??
MSC file should be referred to Microsoft Management Console, you should find it in the registered application index (by choosing the second option in the captured window you sent).
If not locate the application mmc.exe in the %windir%\system32 folder.
Remember to save mmc as the default application to run MSC files.
i just had the same problem. glad i found this post. the reason i had the problem is norton utilities 2002. i uninstalled it and cleaned the registry of all the leftover stuff from it, and had the problem. yout post helped me fix it. i uninstalled nu 2002 because i think it slows the boot process(startup precesses). i could hear my harddisk go thunk thunk like it was going from one end of the disk to the other. if you ever look at the speeddisk map, you probably see some entries at the very end of the disk. speeddisk puts most of that stuff there. during a defrag, ive seen speeddisk move stuff in and out of there.