Hi,
(Why posted in the FAQ-section?)

Are you saying that your program runs but that you can't debug? What in circuit debugger are you using?

I see that you're using a bootloader so I suspect what you actually mean is that you can no longer program the chip thru the bootloader - is that it?
If so, the reason most likely is that the bootloader code is written for a certain oscillator speed (10MHz if that what used to work for you) and when you just change to a 20MHz resonator the bootloader code runs twice as fast as it's supposed to so the baudrate and other timings will off by 100% = no go. Try reprogramming the PIC with a bootloader stub for the correct frequency.

/Henrik.