  In a previous paper, the first two named authors established an isomorphism
between the moduli space of framed flags of sheaves on the projective plane and
the moduli space of stable representations of a certain quiver. In the present
note, we substitute one of the claims made, namely [5, Theorem 17], for a
weaker claim regarding the existence of unobstructed points in the quiver
moduli space. We also extend some of the results of the cited paper, concerning
the maximal stability chamber within which the isomorphism mentioned holds, and
the existence of a perfect obstruction theory for the quiver moduli space.
