  In this paper we study an a posteriori error indicator introduced in E. Dari,
R.G. Duran, C. Padra, Appl. Numer. Math., 2012, for the approximation of the
Laplace eigenvalue problem with Crouzeix-Raviart non-conforming finite
elements. In particular, we show that the estimator is robust also in presence
of eigenvalues of multiplicity greater than one. Some numerical examples
confirm the theory and illustrate the convergence of an adaptive algorithm when
dealing with multiple eigenvalues.
