  Let X be a compact connected Riemann surface of genus at least two. Let r be
a prime number and \xi a holomorphic line bundle on it such that r is not a
divisor of degree(\xi). Let {\mathcal M}_\xi(r) denote the moduli space of
stable vector bundles over X of rank r and determinant \xi. By \Gamma we will
denote the group of line bundles L over X such that $L^{\otimes r}$ is trivial.
This group \Gamma acts on {\mathcal M}_\xi(r). We compute the Chen-Ruan
cohomology of the corresponding orbifold.
