Hi, When using Flip ensure that the BLJB bit is un-ticked else the part will program but upon reset it will run the boot loader and not your code. If this bit is unchecked then ensure that PSEN* is held low long enough after a reset so that the boot-loader is 'engaged'.
Ensure that EA* is pulled high. If left floating it may not go high.
I have used the AC2 and AC3 without any problem.

PS
(Since you are familiar with the AC2 you may have already done this so provide more info)

Tony