[c-nsp] Mixing 2960S and X in stack

[Garry]

Hi,

A customer of ours needed to extend a rack's switch ports, which at that
point consisted of a stack of two 2960S-LPD-L switches. The new switch
he set up was a 2960X-LPD-L. Anyway, contrary to what I would have
expected, neither of the stacking ports on the S and X switches came up.
As the S switches had a rather old 12.2 IOS, I did an update to the
recommended 15.0 SE IOS, which again didn't give me any stacking ports
in state up. Asking around, somebody confirmed they had a mixture of S
and X switches, albeit with an EX train of the IOS. So, I again updated
the S' IOS to the current ED release of the EX train, but still neither
of the switches' stacking even showed any positive change.

Is there anything our customer could be doing wrong, or anything I need
to watch out for as far as configuration goes? I even  tried to manually
provision the X switch on the stack, still no improvement ...

Tnx, -garry