A user here, kindly helping me, told me about the problematic address :

"This address is a multisig address and should have at least 2 private keys, not 1. How did you generate this address ?"

I never asked for a mutlisig address when I created the wallet in Armory, and never asked for a multisig receinving address when asking the Armory wallet to generate me a BTC receiving address...

And when I export privkey, only 1 privkey shows, not 2, as it should be in case of multisig address...

I don't understand.