NAV product code cannot activate when region s different

I bought 10 NEW copies of NAV to apply to new computers (I am a VAR installer), the first 5 worked just fine at ACtivation, but the next 5 won't accept, saying code is invalid, they are legitimite copies but made in Singapore, all in English and even passed the screen at Installation when code was inputted.  This process always works and given me 365 days subscription and suddenly stopped about 2 weeks ago?