I recently downloaded MW II and wanted to update it, have gotten error no: BLZBNTAGT00000870, which basically asks for admin privileges from windows for battle net to make changes.
Tried a bunch of things like logging out/in, launching battle net in admin mode and so on.
Turns out overwatch was trying to update in the background also, cancelled that and it is fine now.
Might be considered a bug since the error was resolved by something completely different in the error text.