Hi,
I had the same problem with the 18F2431, there's a thread about it here. Basicly all I had to do was add a 1k resistor between pin7 and pin11. But I programmed mine IN the PICStart socket and there's notes in the PICStart help file that you must connect ALL the power-pins in order for it to work. Any way, read the above thread and I think you'll be able to get that chip programmed.

/Henrik.