OK, this should be the final word on this.  I only write it because it might
be useful to someone.

Things were still a bit erratic, even after switching to Xwisp2.  So I went
back and carefully read the material on ICSP which Olin Lathrop has posted
at embedinc.com.  In particular, as erratic as my problem seemed to be, I
felt that there could be cross-talk between PGC and PGD occuring.  So I put
a couple of 100 pf capacitors from the input pins on the circuit board, for
those two lines, to ground.  It now seems to be very solid.

(In hindsight, that was probably the problem from the beginning, and
switching to Xwisp2 had nothing to do with it.  However, since I have made
the switch, I'll stick with it now.  Who knows -- I may need the support
for  the newer chips.  :-)

Regards,
Bill
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