  In a diquark-diquark-antiquark picture of pentaquarks, we use two
interpolating currents to calculate the mass of the recently measured
$\Xi^{--}$ state in the framework of QCD sum rules. We show that, even though
yielding similar values for $m_{\Xi^{--}}$ (and close to the experimental
value), these currents differ from each other in what concerns the strength of
the pole, convergence of the OPE and sensitivity to the continuum threshold
parameter.
