John Duncan wrote:

> Admittedly it has seen a lot of write cycles, but nowhere near the
> quoted minimum.  I can read the program memory, but it won't allow a
> write of the program memory.  The data eeprom and config fuses can be
> read and written.

  The usual cause of this problem, at least according to previous posts,
is:  "A bit fell off your programmer!"

  Look for dry joints, check voltages.
--
  Cheers,
        Paul B.