Thanks for replying. I did try booting from every other partition but no luck. I had to reinstall.

I have narrowed down the trigger. When it failed, I was running MOC using a local user without admin rights. Even though I okayed the UAC prompts, it seems something did not complete.

Since then I have done all my MOC work from my local user that does have admin rights, and no problems so far.

I also find that even with the UAC slider switched down to minimum I still get prompted for helper and MOC. So I have returned UAC back to where it should be.

Is there a way to remove the MOC icon from my non-admin account so that I don't inadvertently run it by mistake and trash my working OS?

Thanks!