Uncomplemented uniform algebras

Let $A$ be a closed subalgebra of the algebra of all complex-valued continuous functions on a compact space $X$, and suppose $A$ contains the constant functions and separates points of $X$; let $I$ be a closed ideal of $A$ such that for some linear multiplicative functional $\varphi$ on $A$ we have the relation $0<\|\varphi|_I\|<1$ (for the existence of such an ideal it is sufficient that in the maximal ideal space of the algebra $A$ there exists a Gleason part consisting of at least two points). Then the Banach space $A^{**}$ is not injective [in particular, $A$ is not a complemented subspace of $C(X$)].