  We probe into the instabilities of microscopic quantum black holes. For this
purpose, we study the quasinormal modes (QNMs) for a massless scalar
perturbation of the noncommutative geometry inspired Schwarzschild black hole.
By means of a sixth order Wentzel-Kramers-Brillouin (WKB) approximation we show
that the widely used WKB method does not converge in the critical cases where
instabilities show up at the third order. By employing the inverted potential
method, we demonstrate that the instabilities are an artifact of the WKB
method. Finally, we discuss the usefulness of the asymptotic iteration method
to find the QNMs.
