Ok, now that's really ODD. The config file I posted last night, I changed to Tommy's config and ran it a few more times with no success. This morning, I open the config file and it's changed back to FALSE. I change it to TRUE again... and Mir is there now. So odd problem solves itself oddly.
Could it be connected to that you use Windows Vista/7 and Orbiter is in Program Files, or this isn't your case?