  The identification of non-radial g-mode oscillations as the cause of
variability in cool subdwarf B stars (PG1716 variables) has been frustrated by
a 5 000 K discrepancy between the observed and theoretical blue edge of the
instability domain (Fontaine et al. 2003). A major component in the solution to
this problem has been identified} by (a) using updated OP instead of OPAL
opacities and (b) considering an enhancement of nickel, in addition to that of
iron, in the driving zone. The reason for this success is that, in OP, the
``Fe-bump'' contributions from iron and nickel occur at higher temperatures
than in OPAL. As well as pointing to a solution of an important problem in
stellar pulsation theory, this result provides a critical test for stellar
opacities and the atomic physics used to compute them.
