  We study a system of coincident $D4$ and $\bar D 4$ branes with non zero
world-volume magnetic fields in the weak coupling limit. We show that the
conditions for absence of tachyons in the spectrum coincide exactly with those
found in hep-th/0206041, in the low energy effective theory approach, for the
system to preserve a $\frac 14$ of the supersymmetries of the Type IIA string
theory vacuum. We present further evidence about the stability of the system by
computing the lowest order interaction amplitude from both open and closed
channels, thus verifying the no force condition as well as the supersymmetric
character of the spectrum. A brief discussion of the low energy effective five
dimensional world-volume theory is given.
