  We study fractional D-branes in the Type-IIA theory on a non-compact
orientifold of the orbifold C^3/Z_3 in the boundary state formalism. We find
that the fractional D0-branes of the orbifold theory become unstable due to the
presence of a tachyon, while there is a stable D-instanton whose tachyon gets
projected out. We propose that the D-instanton is obtained after tachyon
condensation. We evidence this by calculating the Whitehead group of the
Abelian category of objects corresponding to the boundary states as being
isomorphic to Z_2.
