Hi ustredna,
What everyone here is trying to explain, but not quite doing is this:
The PIC oscillator requires a bit more power to operate at speeds above 4mhz.
you set the program parameters to be correct in your code for the oscillator speed with your DEFINE OSC 20 statement, but you tell the programmer to enable the oscillator to use the high power setting with the config fuse, or by manualy selecting HS on the programmer's software, elsewise your Oscillator is not going to work.
JS