Wrong! God is totally unable to sin, just like man is totally unable to not sin! And what accounts for this inability is not volition but NATURE, as Cam has recently pointed out! Can the leopard change its spots? Do you think, like Studier does, that spot changing is a merely a matter of will or is it a question of ESSENCE/NATURE? Leopards are carnivores because of an act of their will or because eating flesh and blood inheres in their nature? Do leopards become carnivores after they kill and eat, or do they kill and eat because their own nature compels them to do so?
Likewise, God cannot sin, cannot lie, cannot deny Himself because His HOLY nature compels him to do only what is right, holy and good. Likewise, sinners cannot not sin because their sinful natures compel them to sin.