I think your problem has to be some sort of config issue, Andy. I just spent a whole lot of time scratching my head because a 16F877 will accept an 8 Mhz Xtal as "XT", but a 16F877A will only accept the same clock rate as "HS". With data sheets in 230 page range, it seems like someone at Microchip could have taken the time to compile a short section in the "A" datasheet on the differences between the chips. I guess that would have made it too easy.