Hardware : EB006, HP488 PICmicro programmer boards
When trying to program any of these chips (18F2331, 18F2431, 18F4331, 18F4431) the PPP software reports that the chip has not been erased and then that it has not been verified correctly.
This particular range of 18F PICmicro chips has a hardware defined AVCC pin at pin 7. This pin does not need to be set to allow the chip to run but it does require a 5V input to allow the chip to be reprogrammed.
To supply the AVCC pin with the required 5V input you have to do the following.
HP488: Press and hold switch SA5 while programming.
EB006: Attach a switch E-Block or similar to PortA and wire a connection between +V on the EB006 and the +V on the switch board. Then Press and hold switch SW5 while programming.