This paper studies the vanishing of Ext modules over group rings. Let R be a commutative noetherian ring and ,a group. We provide a criterion under which the vanishing of self extensions of a , nitely generated R,-module M forces it to be projective. Using this result, it is shown that R,satis, es the Auslander-Reiten Conjecture, whenever R has , nite global dimension and ,is a , nite acyclic group.