Why Ring of Exalted Marrow not works on Ansur lich dragon?

[MacKot۞]

It was supposed to be so cool you are a great necromancer you have the power to command the dead a majestic dragon flies into the air ready to strike, but on your finger the ring lights up you order it to lie down and it angrily obeys you and you earn an Achievement to bring it down in flight. But no, he doesn't pass the throw, but he's immune to the effect from somewhere.