- It seems it might be some difference depending on whether the account you're doing this with is roaming or an administrator. At least, a lot of people in the thread thought it would make a difference. Maybe your command prompt works with Arc because it's a different user.
If you find out any more about what's going on, I hope you'll keep us in the loop. :)
Of course, since you already have this working via the command prompt, it's understandable if you prefer not to mess with it.