  When studying a general system of delay differential equation with a single
constant delay, we encounter a certain lack of uniqueness in determining the
coefficient of one of the third order terms of the series defining the center
manifold. We solve this problem by considering a perturbation of the considered
problem, perturbation that allows us to remove the singularity. The result
generalizes a similar result obtained for scalar differential equations (J.
Dyn. Diff. Eqns., 24/2012).
