I have two boards, one board can be programmed to
"force the device to enter ISP mode" usng IAP call
for 89V/LV51Rx2 bootcode enhancements with version
7 of bootloader.

The board that cannot be programmed so has an IC
with the foll description
P89LV51RD2BBC
CS7431.00
kzG0626 AC

What could be the problem, is there any other way
to test the IAP calls.